Processes for the preparation of squarylium dyes

ABSTRACT

Squarylium compounds of the formula:   &lt;IMAGE&gt;   (in which Q1 and Q2 are each a chromophoric group having an aromatic unsaturated system conjugated with the squarylium ring and such that in the compounds of formulae Q1CH2R1 and Q2CH2R2 the methylene hydrogens are active hydrogens, R1 and R2 are each independently a hydrogen atom or an aliphatic or cycloaliphatic group, and R3 and R4 are each independently a hydrogen atom, or an acyl, aliphatic, cycloaliphatic, aromatic or heterocyclic group, subject to the proviso that one of R3 and R4 may be an amino or substituted amino group, or one of R3 and R4 is a hydrogen atom and the other is an organosulfonyl group, or R3 and R4 together with the intervening nitrogen atom form a nitrogenous heterocyclic ring) are useful as near infra-red absorbers. The presence of the amino group on the squarylium ring enables minor changes in absorption wavelength to be achieved by modifications of this group, and also allows functional groups to be incorporated into the dye without changing the chromophoric groups.

REFERENCE TO PARENT APPLICATION

This application is a division of application Ser. No. 08/235,483, filedApr. 29, 1994 (now U.S. Pat. No. 5,492,795), which is a division ofapplication Ser. No. 07/979,250, filed Nov. 20, 1992 (now U.S. Pat. No.5,354,873), which in turn in a continuation-in-part of application Ser.No. 07/795,034, filed Nov. 20, 1991 (now U.S. Pat. No. 5,227,498).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to squarylium dyes, and processes andintermediates for the preparation thereof. More specifically, it relatesto such dyes and intermediates in which the squarylium ring bears anamino or substituted amino group, and also certain other intermediatesuseful for the preparation of the aforementioned dyes.

2. References to Related Applications

U.S. Pat. No. 5,405,976 and International Application No. PCT/US91/08695(Publication No. WO 92/09661) describe dyes comprising an inner salt ofa compound of the formula:

    Q.sup.1 =Z-Z.sup.2

wherein:

Q¹ is a 4-(benz[b]-4H-pyrylium)methylidene,4-(benz[b]-4H-thiopyrylium)methylidene or4-(benz[b]-4H-selenopyrylium)methylidene grouping;

Z is a 1,3-(2-hydroxy-4-oxo-2-cyclobutylidene) or1,3-(2-hydroxy-4,5-dioxo-2-cyclopentylidene) ring; and

Q² is a 4-(benz[b]-4H-pyran-4-ylidene)methyl,4-(benz[b]-4H-thiopyran-4-ylidene)methyl or4-(benz[b]-4H-selenopyran-4-ylidene)methyl grouping;

wherein at least one of the groupings Q¹ and Q² carries at its2-position a substituent in which a non-aromatic carbon atom is bondeddirectly to the benzpyrylium, benzthiopyrylium or benzselenopyryliumnucleus, subject to the proviso that if this 2-substituent contains anaromatic nucleus, this aromatic nucleus is not conjugated with thebenzpyrylium, benzthiopyrylium or benzselenopyrylium nucleus to which itis attached. These dyes have high absorptions in the near infra-red, andimproved solubility in semi-polar solvents and plastics. The dyesdisclosed in these applications include certain infra-red dyes which canbe used in the thermal imaging medium described below with reference toFIG. 6.

Copending application U.S. Ser. No. 07/696,222, filed May 6, 1991 (nowU.S. Pat. No. 5,231,190) and assigned to the same assignee as thepresent application, and the corresponding European Application No.92107574.3, describe and claim the squarylium compounds of formulae D,E, J and K described below with reference to FIG. 1, together withsimilar compounds containing different heterocyclic nuclei, andsquarylium compounds of the formula: ##STR2## wherein Q¹ and Q² are eachindependently a heterocyclic nucleus such that in the compounds offormulae Q¹ CH₂ R¹ and Q² CH₂ R² the methylene hydrogens are activehydrogens, the atoms of Q¹ and Q² which are bonded directly to the CR¹and CR² groupings respectively each being part of an aromatic ring, andQ¹ and Q² are different, and R¹ and R² are each independently a hydrogenatom or an aliphatic or cycloaliphatic group. The disclosure of thiscopending U.S. application is discussed below in more detail withreference to FIG. 1.

Copending applications U.S. Ser. Nos. 07/695,641 (now U.S. Pat. No.5,342,816) 07/696,196 (see also the corresponding European ApplicationNo. 92107576.8 (Publication No. 512,476)) and 07/695,932 (now U.S. Pat.No. 5,153,169, issued Oct. 6, 1992), all filed May 6, 1991 and allassigned to the same assignee as the present application, describe andclaim imaging media comprising a color-forming layer comprising athermal color-forming composition adapted to undergo a change of colorupon increase in the temperature of the color-forming layer above acolor-forming temperature for a color-forming time. Preferred imagingmedia described in these three applications comprise three separatecolor-forming layers containing yellow, cyan and magenta thermalcolor-forming compositions; each of these color-forming compositionscomprises a color-forming compound which undergoes a change of colorupon healing above the color-forming temperature for the color-formingtime, and an infra-red absorber capable of absorbing infra-red radiationand thereby generating heat in the color-forming layer. The threecolor-forming layers use infra-red absorbers absorbing at differingwavelengths so that each color-forming layer can be imagedindependently; for example, specific imaging media disclosed in thesethree applications use infra-red absorbers having peak absorptions atapproximately 792, 822 and 869 nm.

Copending application U.S. Ser. No. 07/795,341, filed Nov. 20, 1991 (nowU.S. Pat. No. 5,206,206), and assigned to the same assignee as thepresent application, describes infra-red dyes generally similar to thoseof the present invention, but in which the 2-substituent on thesquarylium ring has a carbon atom directly bonded to the squaryliumring.

Copending application U.S. Ser. No. 07/795,101, filed Nov. 20, 1991 andassigned to the same assignee as the present application describes andclaims thermal imaging media generally similar to those described in theaforementioned applications U.S. Ser. Nos. 07/695,641; 07/696,196 and07/695,932 but in which at least one imaging layer contains a metalcation. Preferred imaging media described in this application haveimaging layers containing zinc acetate, as described below withreference to FIG. 6.

The disclosures of all the aforementioned copending U.S. applicationsand patents are herein incorporated by reference.

3. Description of the Prior Art

It is known that compounds in which two chromophoric groups are linkedby a pentamethine chain, the three central carbon atoms of which formpart of a squarylium ring are useful as dyes, especially near infra-reddyes. (The term "near infra-red" is used herein to mean electromagneticradiation having a wavelength of about 700 to about 1200 nm.)

The term "chromophoric group" is used herein to mean a group containinga plurality of conjugated unsaturated linkages arranged so that theunsaturated linkages are conjugated with the squarylium ring via theunsaturated (sp²) meso carbon atom lying between the chromophoric groupand the squarylium ring, the chromophoric group being such that thesquarylium dye has substantial absorption of visible or infra-redradiation.

For example, Japanese Patent Application No. 103,604/82 (Publication No.220,143/83, published Dec. 21, 1983), discloses a broad class ofbis-heterocyclic pentamethine dyes in which the central three carbonatoms of the pentamethine chain form part of a squarylium or croconyliumring. The heterocyclic nuclei can be pyrylium, thiopyrylium,selenopyrylium, benzpyrylium, benzthiopyrylium, benzselenopyrylium,naphthopyrylium, naphthothiopyrylium or naphthoselenopyrylium nuclei,which can be substituted with alkyl, alkoxy, aryl or styryl groups.

Japanese Patent Application No. 60-8730 (Publication No. 167,681/86,published Jul. 29, 1986), discloses bis(4-benz[b]thiopyrylium)pentamethine dyes in which the central three carbon atoms of thepentamethine chain form part of a squarylium ring. The dyes are intendedfor use as infra-red absorbers.

U.S. Pat. No. 4,508,811, issued Apr. 2, 1985, describes an opticalrecording element in which the recording layer comprises abis(2,6-dialkyl)-pyrylium or -thiopyrylium squarylium salt.

The squarylium dyes disclosed in these Japanese applications and U.S.patent are capable of achieving high extinction coefficients in the nearinfra-red range. However, such squarylium dyes suffer from a number ofdisadvantages. Many of these prior art dyes have low solubility in mostplastics and/or in semi-polar solvents (for example, methyl ethyl ketoneand methylene chloride) from which they need to be deposited to formimaging media. Thus, it is difficult to dissolve or disperse theabsorber in a plastic without forming large aggregates and withoutadversely affecting other properties of the plastic.

A related disadvantage is that, unless specific functional groups areprovided on the chromophoric groups (and the presence of such functionalgroups on the chromophoric groups may cause problems in the synthesis ofthe compounds from which the chromophoric groups are derived, or in thecondensation of these compounds with squaric acid or its derivatives toform the final dyes), there is no convenient site (or "handle") on thesquarylium dye for attachment of functional groups. Attachment offunctional groups to the squarylium ring may be desirable, for example,to change the solubility of the dye in, or its compatibility with,various media, or to permit the dye to be chemically bonded to othermaterials.

Thirdly, among the squarylium dyes disclosed in these Japaneseapplications and U.S. patent, it may be difficult to find a dye whichabsorbs at the precise wavelength required for a particular application.For example, when choosing infra-red absorbers for use in imaging mediasuch as those described in the aforementioned applications U.S. Ser.Nos. 07/695,641; 07/696,196 and 07/695,932, the need for independentaddressing of the three color-forming layers, coupled with the widths ofthe peaks (typically the full-width-half-maximum (FWHM) of these peaksis about 35-40 nm) and the limited wavelength range over which presentsemiconductor lasers can be produced economically, mean that it is oftennecessary to find an infra-red absorber which has an absorption peakwithin a very narrow range (say 10-15 nm) and which meets all the otherrequirements of stability, solubility and compatibility with othercomponents of the imaging medium required for use in such an imagingmedium. It is often difficult if not impossible to find a squarylium dyefrom among those disclosed in the Japanese applications and U.S. patentwhich absorbs within such a narrow wavelength range.

The aforementioned disadvantages of earlier prior art squarylium dyesare greatly reduced in the dyes described in the aforementionedapplications U.S. Ser. Nos. 07/616,639, 07/795,038 and 07/696,222. The2-non-aromatic substituted dyes described in applications U.S. Ser. Nos.07/616,639 and 07/795,038 are substantially more soluble than thecorresponding 2-phenyl dyes, while the asymmetric dyes which can besynthesized in good yields by the processes described in applicationU.S. Ser. No. 07/696,222 greatly ease the task of finding a dye whichabsorbs at a desired wavelength, since the ability to change the twochromophoric groups independently gives an additional degree of freedom,as compared with earlier dyes in which the two chromophoric groups werethe same. However, neither of these copending applications describesdyes in which functional groups are provided on the squarylium ringitself. Furthermore, there are still situations in which it would beadvantageous to provide dyes with even greater solubility in certainmedia than those described in applications U.S. Ser. Nos. 07/616,639 and07/795,038, and it would also be advantageous to provide some way inwhich the dyes disclosed in applications U.S. Ser. Nos. 07/616,639,07/795,038 and 07/696,222 could be "fine tuned" by shifting theirinfra-red absorption peaks over small ranges (say 30 nm) in order toassist in providing dyes having absorptions within very narrow desiredranges.

It has now been found that providing an amino or substituted amino groupin place of one of the oxygen atoms of the squarylium ring in squaryliumdyes (the resulting dye being hereinafter referred to as an"aminosquarylium" dye) allows the absorption peak of the dye to beshifted somewhat, allows various functional groups to be incorporatedconveniently into the dye, and may increase the solubility of the dyein, or its compatibility with, certain media. The amino group on thesquarylium ring also provides a potential means for chemically bondingthe dye to other materials. Accordingly, this invention is directed tothese aminosquarylium dyes, to processes and intermediates for thepreparation of such dyes, and to processes and imaging media containingthese dyes.

SUMMARY OF THE INVENTION

This invention provides a squarylium compound of the formula: ##STR3##in which Q¹ and Q² are each a chromophoric group having an aromaticunsaturated system conjugated with the squarylium ring and such that inthe compounds of formulae Q¹ CH₂ R¹ and Q² CH₂ R² the methylenehydrogens are active hydrogens, R¹ and R² are each independently ahydrogen atom or an aliphatic or cycloalkyl group, and R³ and R⁴ areeach independently a hydrogen atom, or an acyl, aliphatic,cycloaliphatic, aromatic or heterocyclic group, subject to the provisothat one of R³ and R⁴ may be an amino or substituted amino group, or oneof R³ and R⁴ is a hydrogen atom and the other is an organosulfonylgroup, or R³ and R⁴ together with the intervening nitrogen atom form anitrogenous heterocyclic ring.

The squarylium compounds of Formula I in which one of R³ and R⁴ is(notionally) a hydrogen atom and the other is an organosulfonyl group(i.e., in which a --SO₂ NH-- grouping is directly attached to thesquarylium nucleus) (these compounds are typically encountered in theirdeprotonated form) can be synthesized in a manner which is differentfrom that employed for the other squarylium compounds of Formula I, inthat introduction of the sulfonamide group can be effected directly intothe unsubstituted squarylium dye. Accordingly when hereinafter it isnecessary to distinguish the two groups of compounds, the squaryliumcompounds of Formula I in which one of R³ and R⁴ is (notionally) ahydrogen atom and the other is an organosulfonyl group will be referredto as the "sulfonamide" compounds of Formula I, while the remainingcompounds of Formula I will be referred to as the "non-sulfonamide"compounds. It should be noted that compounds of the present invention inwhich one of R³ and R⁴ is a sulfonated alkyl group are non-sulfonamidecompounds.

This invention also provides a squaric acid derivative of the formula:##STR4## in which Q¹ is a chromophoric group having an aromaticunsaturated system conjugated with the squarylium ring and such that inthe compound of formula Q¹ CH₂ R¹ the methylene hydrogens are activehydrogens, R¹ is a hydrogen atom or an aliphatic or cycloaliphaticgroup, and R³ and R⁴ are each independently a hydrogen atom, or an acyl,aliphatic, cycloaliphatic, aromatic or heterocyclic group, subject tothe proviso that one of R³ and R⁴ may be an amino or substituted aminogroup, or R³ and R⁴ together with the intervening nitrogen atom form anitrogenous heterocyclic ring.

This invention also provides a process for the preparation of a squaricacid derivative of Formula II, which process comprises reacting acorresponding squaric acid derivative of the formula: ##STR5## in whichA is a chlorine or bromine atom, or an alkoxyl group, and Q¹ and R¹ areas defined above, with ammonia or a compound of formula NHR³, NHR⁴, orNHR³ R⁴, in which R³ and R⁴ are as defined above. This process mayhereinafter be referred to as the "first process of the invention".

This invention also provides a process for the preparation of asquarylium compound of Formula I above, which process comprises reactinga corresponding squaric acid derivative of Formula (II) above, in whichQ¹, R¹, R³ and R⁴ are as defined above, with a compound of the formulaQ² CH₂ R², in which Q² and R² are as defined above. This process mayhereinafter be referred to as the "second process of the invention".

This invention also provides a process for the preparation of asulfonamide squarylium compound of Formula I above, which processcomprises reacting the corresponding squarylium compound of the formula:##STR6## in which Q¹, Q², R¹ and R² are as defined above, with thecorresponding organosulfonyl isocyanate. This process may hereinafter bereferred to as the "third process of the invention".

This invention also provides a process for the preparation of anon-sulfonamide squarylium compound of Formula I above, which processcomprises reacting a corresponding squaric acid monoester monoamide withat least one compound of formula Q¹ CH₂ R¹ or Q² CH₂ R². This processmay hereinafter be referred to as the "fourth process of the invention".

This invention also provides a process for the preparation of a squaricacid derivative of Formula II above, which process comprises reacting acorresponding squaric acid monoester monoamide with a compound offormula Q¹ ═CHR¹. This process may hereinafter be referred to as the"fifth process of the invention".

This invention also provides a process for the preparation of a1,3-disubstituted-2-amino or substituted amino squarylium dye, whichprocess comprises reacting the corresponding1,3-disubstituted-2-unsubstituted squarylium dye with an alkylatingagent to produce a corresponding 1,3-disubstituted-2-alkoxy squaryliumcompound, and thereafter reacting the 2-alkoxy compound with ammonia ora primary or secondary amine to produce the 1,3-disubstituted-2-amino orsubstituted amino squarylium dye. This process may hereinafter bereferred to as the "sixth process of the invention".

This invention also provides a compound of the formula: ##STR7## whereinR¹, R² and R¹ are each independently a hydrogen atom or an aliphatic orcycloaliphatic group, and Q³ and Q⁴ are each independently a pyrylium,thiopyrylium, selenopyrylium, benzpyrylium, benzthiopyrylium orbenzselenopyrylium nucleus. These compounds may hereinafter be referredto as the "2-alkoxy compounds" of the present invention.

This invention also provides a process for generating heat in a mediumcomprising a dye of the present invention, which process comprisesexposing at least part of the medium to infra-red actinic radiation of afrequency absorbed by the dye, whereby the radiation is absorbed by thedye and heat is generated within the parts of the medium exposed to theradiation.

Finally, this invention provides a thermal imaging medium comprising atleast one imaging layer, the imaging layer comprising a color-formingcompound which undergoes a change of color upon heating above acolor-forming temperature for a color-forming time, the imaging layerfurther comprising a dye of the present invention.

It will be noted that the symbol Q¹ has been used for both a divalentgrouping in Formulae I, II, III and IV, and a monovalent grouping in theformula Q¹ CH₂ R¹. This apparent anomaly is due to the fact that thebond orders in the compounds of Formula I, II, III and IV are notintegral. For example, the dye A shown in FIG. 2 of the accompanyingdrawings is actually a resonance hybrid of the form shown and thesimilar form in which the positive charge resides on the oxygen atom ofthe other benzpyrylium nucleus (with contributions from other resonanceforms). Thus, whether Q¹ is drawn as divalent or monovalent dependssolely upon which of the contributing resonance forms is drawn, andsimilarly for Q². On the other hand, the compounds of formula Q¹ CH₂ R¹,such as the salt B shown in FIG. 1, are not resonance hybrids to anysignificant extent, and thus in this formula Q¹ is correctly shown asmonovalent. The Q¹ /Q² nomenclature employed will thus be clear toskilled chemists. Similar considerations apply to Q³ and Q⁴.

When either R³ or R⁴ in the compounds of Formulae I and II is hydrogen,the hydrogen atom(s) attached to the nitrogen are of course susceptibleto being removed by bases, and the compounds may thus be encountered indeprotonated forms depending upon the pH of the medium containing thecompound. Although the compounds of Formulae I and II are normally shownherein in their protonated forms, the invention extends to thedeprotonated forms of these compounds. In particular, the sulfonamidecompounds of Formula I are so readily deprotonated that they will oftenbe found in their deprotonated form under neutral conditions. Thediscussion in the following four paragraphs assumes that the compoundsof Formula I are present in their protonated form, but the consequencesof deprotonation of the compound will readily be apparent to skilledchemists.

The compounds of Formula I produced by the processes of the presentinvention may be cationic, anionic or non-ionic. When none of thechromophoric groups Q¹ and Q² and the substituents R¹, R², R³ and R⁴carries any charged substituents, the Q¹ Q² -aminosquarate moiety(hereinafter referred to simply as the "dye moiety") bears a singlepositive charge, and hence the dye is cationic. However, any one or moreof the chromophoric groups Q¹ and Q² and the substituents R¹, R², R³ andR⁴ may carry a negatively or positively charged group (for example a--COO⁻ or triialkylammonium substituent), and if one or more negativelycharged substituents is present, the dye will be non-ionic or anionicrespectively.

When a counterion is present in a cationic or anionic dye of the presentinvention, the counterion may be any counterion which is notincompatible with the dye moiety and which thus provides a stable salt.The choice of counterion may be important in ensuring the solubility ofthe dye in various media, and reducing or preventing aggregation of thedye; minimizing aggregation of the dye is highly desirable since suchaggregation can significantly reduce the apparent extinction coefficientof the dye in polymeric media.

Similarly, if the chromophoric group Q¹ or Q¹ does not carry any chargedsubstituents (such nuclei being generally preferred in the presentprocesses), the "compounds" Q¹ CH₂ R¹ and Q² CH₂ R² used in the presentprocesses are actually cations. The counterion present may be anycounterion which provides a stable salt and which does not interferewith the relevant reactions. Typically, large fluorinated anions, suchas trifluoromethane sulfonate and tetrafluoroborate have been found togive good results in the present processes. The groups Q¹ and Q² may;however, bear charged substituents and thus in some cases Q¹ CH₂ R¹ andQ² CH₂ R² may be neutral compounds which do not require the presence ofa counterion.

It may often be found convenient, for synthetic reasons, to prepare adesired moiety with one counterion and thereafter to effect a counterionexchange to form a different salt of the same moiety. Methods for suchcounterion ion exchange are well known to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the accompanying drawings shows a synthetic scheme for thepreparation of a staring material of Formula III used in the presentinvention by reactions described in the aforementioned application U.S.Ser. No. 07/696,222;

FIG. 2 shows the conversion of a starting material of Formula III to asquaric acid derivative of Formula II and thence to a squaryliumcompound of Formula I by the first and second processes of the presentinvention;

FIG. 3 shows the synthesis of a squarylium compound of Formula I from acorresponding squaric acid monoester monoamide by the fourth process ofthe present invention;

FIG. 4 shows the preparation of an exo-alkylene compound of the presentinvention by the fifth process of the present invention, and thecondensation of this exo-alkylene compound with a squaric acid monoestermonoamide to produce the same type of intermediate as shown in FIGS. 2and 3;

FIG. 5 shows the conversion of a 2-unsubstituted squarylium dye to acorresponding 2-aminosquarylium dye by the sixth process of the presentinvention; and

FIG. 6 shows a schematic cross-section through a preferred imagingmedium of the present invention incorporating infra-red dyes of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The interrelationships among the various reactions of the presentinvention may best be seen from the accompanying drawings. FIGS. 1 and 2show a synthetic scheme for the preparation of a squarylium compound(hereinafter referred to as "Dye A") of Formula I, in which Q¹ is (inthe resonance hybrid drawn) a7-diethylamino-2-(1,1-dimethylethyl)-(benz[b]-4H-pyran-4-ylidene)grouping and Q² is a4-[7-diethylamino-2-(1,1-dimethylethyl)-benz[b]pyrylium] grouping. Thereactions shown in FIG. 1 are described in the aforementionedapplication U.S. Ser. No. 07/696,222, while the reactions shown in FIG.2 are examples of the first and second processes of the presentinvention. Accordingly, the reactions shown in FIG. 1 will only bebriefly described herein, and for fuller details the reader is referredto the copending application U.S. Ser. No. 07/696,222.

One form of the synthesis begins with the condensation of a2,6-bis-(1,1-dimethylethyl)-4-(R¹ -methyl)-7-diethylaminobenzpyryliumsalt B (a compound of Formula Q¹ CH₂ R¹) with2,3,4,4-tetrachlorocyclobut-1-en-2-one C to give the trihalosquaric acidderivative D. The tetrachloro compound C and its synthesis are describedin Maahs et al., "Syntheses and Derivatives of Squaric Acid", Angew.Chem. Int. Ed., 5, 888-893 (1966). This reaction is conducted in thepresence of a base, preferably triethylamine. As noted above, the anionof the salt B can be any anion which provides a stable salt and whichdoes not interfere with the desired reaction; conveniently thetetrafluoroborate salt is used.

As may be seen from FIGS. 1 and 2, use of the 4-methylbenzpyrylium saltB (R¹ is a hydrogen atom) will produce a dye in which R¹ is hydrogen. Ifthe 4-methyl group of the salt B is replaced with a different group ofthe formula --CH₂ R¹, the corresponding dyes can be produced in which R¹is an aliphatic or cycloaliphatic group; thus, for example, the use of a4-ethyl salt gives a final dye in which R¹ is methyl. Similar variationsin the group R² may be produced by varying the 4-substituent in thebenzpyrylium salt of Formula M (described below). The tetrabromohomologue may be used in place of the tetrachloro compound C.

In the next step of the synthesis, the trihalosquaric acid derivative Dis hydrolyzed to the corresponding non-halogenated derivative E.Desirably, this hydrolysis is effected by heating the derivative D withtriflic acid, then adding water.

Alternatively, the non-halogenated derivative E may be prepared bycondensing the salt B with the diacid chloride (F), an ester/acidchloride (G) or a diester (H) of squaric acid (the butyl ester/acidchloride and diester are shown in FIG. 1), followed by hydrolysis of theresultant product. With both the monoacid chloride/monoester G and thediester H, this reaction requires the presence of a base to produceuseful yields; with the more reactive diacid chloride F, this reactioncan be conducted without base. The reaction of the diacid chloride F mayalso be promoted by a Lewis acid.

When the diacid chloride F is used as starting material in thisreaction, the intermediate is J, the acid chloride of E, whereas whenthe diester H is used as starting material, the intermediate is K, theester of E. When the ester/acid chloride G is used, both J and K areproduced, but the production of this mixture poses no problems, sinceboth compounds are readily hydrolyzed to give the derivative E. Ifdesired, the add chloride J may be treated with methanol to convert itto the ester K. Add bromides may be used in place of the acid chlorides,and the group R¹ may be varied by changing the 4-substituent on the saltB, as described above.

In FIG. 2 there is shown the first process of the invention, namely thereaction of the ester K with a nitrogen compound of formula HNR³ R⁴ toproduce the corresponding amino squaric acid derivative L. Although theester K has been shown in FIG. 2, this reaction may also be conductedusing the acid chloride J shown in FIG. 1.

The final step of the synthesis of the squarylium dye A is an example ofthe second process of the present invention, namely the condensation ofthe squaric acid derivative L with one mole of the appropriate compoundof formula Q² CH₂ R² ; the compound in which Q² is a2-(1,1-dimethylethyl)-7-diethylaminobenzpyrylium group is shown in FIG.2. The conditions required for this reaction may be substantially thesame as those used for the prior art reactions in which two moles of abenzpyrylium salt are condensed with squaric acid to form a symmetricbisbenzpyrylium dye. Thus, this reaction is assisted by base,conveniently a tertiary amine, for example quinoline. The reaction isdesirably conducted in solution in an alcohol, conveniently butanol.Alternatively, this reaction may be promoted by a Lewis acid, forexample a titanium tetrahalide, conveniently in dichloromethane.

Although the reaction L→A illustrated in FIG. 2 produces a dye A inwhich Q¹ is the same as Q², it will readily be apparent that this neednot be the case, since the group Q¹ derived from compound B (FIG. 1)could be different from the group Q² derived from compound M. Thus, thesynthesis shown in FIGS. 1 and 2 can be used to produce both symmetricdyes, in which Q¹ and Q² are the same, and asymmetric dyes in whichthese two groups are different.

In many cases, the synthesis of the final aminosquarylium dye is mostsimply achieved by introducing the final NR³ R⁴ group during thepreparation of the compound L; for example, when each of R³ and R⁴ is ahydrogen atom or an alkyl group, so that the compound HNR³ R⁴ is ammoniaor a primary or secondary amine, the reaction K→L proceeds well withammonia or a primary or secondary amine so that there is no difficultyin incorporating the final NR³ R⁴ group in this step of the synthesis.However, in other cases, the substituents R³ and R⁴ may be such thatthey interfere with the reaction L→A. In such circumstances it ispreferred to use a different compound HNR³ R⁴ in the reaction K→L, andthen to modify R³ and/or R⁴ in the final dye A. For example, asillustrated in Example 21 below, if one of R³ and R⁴ is to be a hydrogenatom and the other an acyl group, it is convenient to carry out thereaction K→L with ammonia, thereby producing an intermediate L and a dyeA in which both R³ and R⁴ are hydrogen atoms, and then to react this dyeA with the appropriate acyl chloride (or other acyl halide) to attachthe desired acyl group to the amine substituent.

Furthermore, as discussed in more detail below, the groups R³ and R⁴ maycontain various functional groups, and some of these functional groupsmay be capable of interfering with one or both of the reactions K→L andL→A. For example, the reaction L→A depends upon the presence of activehydrogens in the compound Q² CH₂ R², and any functional groups withinthe groups R³ and R⁴ which contain active hydrogens may interfere withthis reaction. In such cases, it may be necessary to modify thesynthesis shown in FIG. 2 either by modifying the group R³ and/or R⁴ inthe dye A (in the same manner as discussed above for the case where R³or R⁴ is an acyl group), or by blocking the functional groups in thecompound HNR³ R⁴ and then unblocking these groups in the dye A.

FIG. 3 shows an alternative synthesis of a dye N starting from a diesterP of squaric acid (the diethyl ester is illustrated in FIG. 3) and usingthe fourth reaction of the present invention. The diester P is firstcondensed with a compound of formula HNR³ R⁴ to introduce an aminogroup, thereby producing the corresponding squaric acid monoestermonoamide Q, which is then condensed with two moles of a compound R offormula Q¹ CH₂ R¹ (the salt in which Q¹ is a2,6-bis(1,1-dimethylethyl)thiopyrylium group is illustrated in FIG. 3)to produce the final symmetrical dye N. The reaction Q→N may be carriedout under the same conditions as the reaction L→A described above withreference to FIG. 2. Also, the synthesis shown in FIG. 3 may be modifiedto include changes in the group R³ and/or R⁴ in the dye N, and theblocking of functional groups, as discussed above with reference to FIG.2.

At present, the synthetic route shown in FIG. 2 is preferred over thatshown in FIG. 3 because the former tends to give better yields of dyeand because the former is capable of producing asymmetric dyes in goodyield. (Although theoretically the synthesis shown in FIG. 3 might bemodified to produce asymmetric dyes by treating the monoester monoamideQ with a mixture of two different compounds Q¹ CH₂ R¹ and Q² CH₂ R²,this approach is not recommended, since the separation of the resultantmixture of three dyes (two symmetric dyes and the desired asymmetricdye) is likely to be very difficult.)

FIG. 4 illustrates the preparation of an intermediate U, which isanalogous to the intermediate L shown in FIG. 2, by a synthetic routewhich exemplifies the fifth process of the present invention andproceeds via an exo-alkylene compound. The synthesis shown in FIG. 4begins from a chromone S; this chromone can be prepared by a variety ofprocesses known to persons skilled in the art of organic synthesis.Certain methods for the synthesis of such chromones are exemplifiedbelow, and other are described in the aforementioned copendingapplications Ser. Nos. 07/616,639 and 07/795,038. The chromone S isfirst converted to the corresponding exo-methylene compound T by meansof a Peterson olefination, as described in, for example, OrganicReactions, Vol. 38, 1-225 (Wiley, New York, 1990); alternatively theexo-methylene compound may be produced by treating the correspondingcompound of formula Q¹ CH₂ R¹ with a strong base. The exo-methylenecompound T is then reacted with a squaric acid monoester monoamide toproduce the intermediate S; this reaction is somewhat analogous to thereaction Q+R→N shown in FIG. 3, but only monocondensation occurs, sothat the intermediate S is analogous to the intermediate L shown in FIG.2. The conversion of T to U is desirably catalyzed by a Lewis acid,preferably an aluminum halide such as aluminum chloride. It will readilybe apparent that the intermediate L can readily be converted to a dye ofthe present invention by a reaction analogous to L+M→A shown in FIG. 2.

In at least some cases, the dyes of Formula I cannot be synthesized byreacting the corresponding dye having an unsubstituted squaryliumnucleus with an amino compound, since in these cases the amino compoundsimply adds reversibly to the squarylium dye. However, unsubstitutedsquarylium dyes can be converted to aminosquarylium dyes of the presentinvention by the indirect route shown in FIG. 5, which illustrates thesixth process of the present invention. In this indirect route, anunsubstituted squarylium dye V is first treated with an alkylatingagent, preferably a dialkyl sulfate, to produce the corresponding2-alkoxysquarylium compound W, and this 2-alkoxy compound is thentreated with a compound of formula HNR³ R⁴ (typically ammonia or aprimary or secondary amine; butylamine is shown for purposes ofillustration in FIG. 5) to produce the final aminosquarylium dye.

The syntheses shown in FIGS. 2-5 are primarily intended for preparingnon-sulfonamide dyes of the present invention. The sulfonamide dyes ofthe present invention are conveniently synthesized by treating thecorresponding squarylium dye with the appropriate organosulfonylisocyanate, with elimination of carbon dioxide; for example tosylisocyanate (p-CH₃ --C₆ H₄ --SO₂ NCO) converts a squarylium dye to thecorresponding p-tolylsulfonamido squarylium dye. This reaction proceedsreadily in solution in a non-polar solvent, for example toluene, nocatalyst being required. The reaction is not confined to aromaticsulfonyl isocyanates and can be carried out with alkyl sulfonylisocyanates, for example butylsulfonyl isocyanate.

As already indicated, a wide range of groups R³ and R⁴ can be present inthe squarylium dyes of the present invention. Thus, for example, R³ andR⁴ can each independently be a hydrogen atom or an acyl, aliphatic,cycloaliphatic, aromatic or heterocyclic group, subject to the provisothat one of R³ and R⁴ may be an amino or substituted amino group, or oneof R³ and R⁴ can be a hydrogen atom and the other be an organosulfonylgroup, such as a tosylsulfonyl group. For example, R³ and R⁴ can each bean alkyl, alkenyl, alkynyl, cycloalkyl (for example, a cyclohexyl group)or cycloalkenyl group, a polycyclic saturated group such as a decalinylor adamantyl group, or a similar group containing ethylenic unsaturation(for example a 6,6-dimethylbicyclo[3.1.1.]hept-2-en-2-yl orbicyclo[2.2.1]hept-2-en-5-yl group) an aromatic group (for example, aphenyl group), or a saturated or unsaturated heterocyclic group (forexample, a piperidino group). In addition, R³ and R⁴, together with theintervening nitrogen atom, may form a nitrogenous heterocyclic ring;thus, for example, the NR³ R⁴ grouping could be a piperidino or indolinogroup, and may contain additional hetero atoms, as for example in amorpholino or pyrimidino group. One of R³ and R⁴ can also be an amino orsubstituted (for example, alkyl or cycloalkyl substituted) amino group,so that the NR³ R⁴ grouping may be a substituted or unsubstitutedhydrazine grouping, for example a trimethylhydrazine grouping.

Any of these groups R³ and R⁴ may be unsubstituted or substituted; asindicated above, it is one of the advantages of the dyes of the presentinvention that the nitrogen on the squarylium ring, and the groups R³and R⁴ attached thereto, provide convenient sites to which a variety ofgroups may be attached in order to modify the properties of the dye,without having to change the chromophoric groups Q¹ and Q². Thus, thegroups R³ and R⁴ may contain substituents which affect the solubility ofthe dye in various media. For example, if it desired to increase thesolubility of the dye in highly polar solvents, the groups R³ and R⁴ maycontain sulfonic acid, carboxyl or quaternary ammonium groups. On theother hand, if it desired to increase the solubility of the dye innon-polar solvents, the groups R³ and R⁴ may be unsubstituted long-chainalkyl groups. The groups R³ and R⁴ may also contain substituents such ashalo, cyano, amino, oxo and phenyl groups, ether, amide and urethanelinkages.

The groups R³ and R⁴ may also contain groups which permit linking thedye to other materials, thereby permitting, for example, the dye to beincorporated into a polymer.

The groups R³ and R⁴ also affect the spectrum of the squarylium dye. Ingeneral, the wavelength (λ_(max)) of maximum absorption of the dye inthe near infra-red becomes longer as the groups R³ and R⁴ become moreelectron donating. For example, in the dyes A shown in FIG. 2, thevariation of λ_(max) with changes in the NR³ R⁴ group is as follows:

    ______________________________________                                        NR.sup.3 R.sup.4                                                                              λ.sub.max, nm                                          ______________________________________                                        NH.sub.2        797                                                           NHCH.sub.2 CH.sub.2 SO.sub.3 .sup.-                                                           810                                                           N(C.sub.2 H.sub.5).sub.2                                                                      828                                                           ______________________________________                                    

The corresponding unsubstituted squarylium dye, in which the group NR³R⁴ is replaced by O⁻, has λ_(max) =808 nm. Thus, in this series of dyes,modification of the unsubstituted squarylium dye by incorporation ofthese amino groups permits modification ("fine tuning") of λ_(max) overa range of -11 to +20 nm.

The value of λ_(max) is also affected by deprotonation of the dye. Asmentioned above, if R³ and/or R⁴ in Formula I is a hydrogen atom, thishydrogen atom may be removed by bases. As shown in Example 54 below,such deprotonation of the dye typically shifts λ_(max) about 60 nmlonger. Thus, in cases where it is desired to provide absorption atlonger wavelengths, it may be advantageous to incorporate a dye of thepresent invention in a basic medium, either by using a basic binder insuch a medium or by providing a separate base in the medium, such thatthe dye exists in the medium in its deprotonated form.

Although the invention has been shown in the accompanying drawings anddescribed above with reference to compounds in which Q¹ and Q² are eacha pyrylium or benzpyrylium nucleus, it will be apparent that both Q¹ andQ² can each independently be any chromophoric group such that in thecompounds of formulae Q¹ CH₂ R¹ and Q² CH₂ R² the methylene hydrogensare active hydrogens, so that these methylene hydrogen atoms can undergothe condensations with squaric acid derivatives already described. It ispreferred that the atoms of Q¹ and Q² which are bonded directly to theCR¹ and CR² groupings respectively each be part of an aromatic ring. Forexample, Q¹ and Q² may each independently be an imidazole,benzimidazole, thiazole, benzthiazole, oxazole, benzoxazole, 2- or4-pyridinium, 2- or 4-quinolinium or indolinium nucleus. Desirably, atleast one, and preferably both, of Q¹ and Q² is a non-nitrogenousheterocyclic nucleus, especially preferred nuclei being pyrylium,thiopyrylium, selenopyrylium, benzpyrylium, benzthiopyrylium andbenzselenopyrylium nuclei. Such nuclei be either the 2- or 4-isomers,although the latter are preferred.

In one preferred group of dyes of Formula I, Q¹ and/or Q² is a2,6-dialkylpyrylium, -thiopyrylium or -selenopyrylium nucleus, in whicheach of the alkyl groups contains not more than about 8 carbon atoms,especially those in which Q¹ and/or Q² is a 2,6-di-tertiarybutylpyrylium, -thiopyrylium or -selenopyrylium nucleus. The presence ofthese nuclei in the dyes has been found to provide good solubility inpolymeric media and high extinction coefficients.

Another preferred group of dyes of Formula I are those in which Q¹and/or Q² is a 4-benzpyrylium, 4-benzthiopyrylium or4-benzselenopyrylium nucleus, desirably such a nucleus which carries atits 2-position a substituent in which a non-aromatic carbon atom isbonded directly to the benzpyrylium nucleus, subject to the proviso thatif this 2-substituent contains an aromatic nucleus, this aromaticnucleus is not conjugated with the benzpyrylium nucleus. The2-substituent may be, for example:

a. an alkyl group, for example an isopropyl, sec-butyl, tert-butyl,2-ethyl-2-methylbutyl or 2,2-dimethylbutyl group;

b. an alkenyl group, for example a vinyl group;

c. an alkynyl group, for example an ethine group;

d. a cycloalkyl group, for example a cyclohexyl group;

e. a cycloalkenyl group, for example a cyclohexenyl group;

f. a polycyclic saturated hydrocarbon group, for example a decalinyl oradamantyl group;

g. a polycyclic, ethylenically unsaturated hydrocarbon group, forexample a 6,6-dimethylbicyclo[3.1.1]hept-2-en-2-yl orbicyclo[2.2.1]hept-2-en-5-yl group;

h. any of the foregoing substituents substituted with aryl, halo, cyano,amino or oxo groups, or containing ether, amine or urethane linkages.The 2-substituent is desirably one in which the carbon atom which isdirectly attached to the benzpyrylium nucleus carries not more than onehydrogen atom.

The benzpyrylium nucleus may also carry at its 7-position a substituentin which an element of Group 5A, 6A or 7A of the Periodic Table isdirectly connected to the benzpyrylium nucleus, subject to the provisothat when this element of Group 5A or 6A, the 7-substituent may be atleast one saturated ring containing this element of Group 5A or 6A, thissaturated ring optionally being fused to the phenyl ring of theassociated benzpyrylium nucleus. Preferred 7-substituents are alkoxygroups containing not more than about 12 carbon atoms, or disubstitutedamine or disubstituted phosphino groups, wherein each of thesubstituents on the or each disubstituted group comprises an alkyl groupcontaining not more than about 6 carbon atoms, or the two substituentson any one disubstituted group together form, with the nitrogen orphosphorus atom thereof, a heterocyclic ring system, this ring systemoptionally being fused to the benzpyrylium nucleus which carries thedisubstituted amine or phosphino substituent. Examples of suitable7-substituents include dialkylamino wherein each of the alkyl groupscontains not more than about 4 carbon atoms, piperidino, indolinyl,morpholino and --N[--(CH₂)₃ --]₂ groups, subject to the proviso thatwhen one or both of the amine groups is a --N[--(CH₂)₃ --]₂ group, theends of the trimethylene groups remote from the nitrogen atom are joinedto the 6- and 8-positions of the benzpyrylium nucleus carrying thenitrogen atom, so that the --N[--(CH₂)₃ --]₂ group and the benzene ringof the benzpyrylium nucleus together form a julolidine ring system. Asdescribed in the aforementioned applications U.S. Ser. Nos. 07/616,639and 07/795,038, dyes containing such 4-benzpyrylium nuclei havedesirable properties, including solubility in polymeric media and highextinction coefficients.

Alternatively, the or each benzpyrylium nucleus may carry at its6-position an alkoxy, alkenyloxy or alicyclyloxy group; the alkyl,cycloalkyl or alicyclic portion of this group may be any of the groups(other than alkynyl) mentioned above as the 2-substituent. Desirably the6-substituent is an alkoxy or cycloalkoxy group, preferably a branchedchain alkoxy group. Specific preferred branched chain alkoxy groups arepropoxy, but-2-oxy and 2-ethylbutoxy groups. Preferably, the benzenering of the benzpyrylium nucleus bears no substituents other than the6-substituent. It has been found that providing such a branched-chain6-substituent increases the solubility of the dye in polymeric media. Inaddition, such 6-substituted dyes tend to have relatively low visibleextinction and are thus advantageous for use in applications (such asthermal imaging media) where visible absorption is undesirable. It isbelieved (although the invention is in no way limited by this belief)that the advantageous solubility properties of the aforementioned6-substituted dyes are due at least in part to the 6-substituentextending out of the plane of the aromatic nucleus to which it isattached, and thus the choice of a 6-substituent may be influenced bythe stereochemistry of the substituent, not merely its chemical nature.

Although R¹ and R² may be other groups, for example cycloalkyl groups orany of the other aliphatic and cycloaliphatic groups discussed above aspotential 2-substituents on benzpyrylium groups Q¹ and Q², it ispreferred that these two groups each independently be a hydrogen atom oran alkyl group containing not more than about 6 carbon atoms.

Specific preferred dyes of Formula I are those in which:

a. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, and R¹, R², R³ and R⁴ are each a hydrogen atom, namely, a4-[[2-amino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumsalt;

b. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ and R⁴ are each an ethyl group and R¹ and R² are each ahydrogen atom, namely a4-[[2-diethylamino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumsalt;

c. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q¹ is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ is a butyl group and R¹, R² and R⁴ are each a hydrogenatom, namely a4-[[2-butylamino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumsalt;

d. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ is a --CH₂ CH₂ SO₃ H grouping, and R¹, R² and R⁴ are each ahydrogen atom, namely the4-[[2-[3-sulfonatoprop-1-ylamino]-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliuminner salt;

e. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ is a pivaloyl grouping and R¹, R² and R⁴ are each ahydrogen atom, namely a4-[[3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-pivaloylamino-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumsalt;

f. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping,Q² is a 4-[2,6-bis(1,1-dimethylethyl)-4H-thiopyrylium] grouping, and R¹,R², R³ and R⁴ are each a hydrogen atom, namely a4-[[2-amino-3-[[2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumsalt;

g. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping,Q² is a 4-[2,6-bis(1,1-dimethylethyl)-4H-thiopyrylium] grouping, R¹ is amethyl group, and R², R³ and R⁴ are each a hydrogen atom, namely a4-[[2-amino-3-[1-[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]-eth-1-yl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]thiopyryliumsalt;

h. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping,Q² is a 4-[2,6-bis(1,1-dimethylethyl)-4H-thiopyrylium] grouping, R³ is aCH₃ CH₂ CH₂ CH₂ SO₂ -- grouping, and R¹, R² and R⁴ are each a hydrogenatom, namely the4-[[3-[[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-butanesulfonylamino-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]thiopyryliumhydroxide inner salt;

i. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping,Q² is a 4-[2,6-bis(1,1-dimethylethyl)-4H-thiopyrylium] grouping, R³ is abutyl group and R¹, R² and R⁴ are each a hydrogen atom, namely a4-[[2-butylamino-3-[[2,6-bis[1,1-dimethylethyl]thiopyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]thiopyryliumsalt;

j. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping,Q² is a 4-[2,6-bis(1,1-dimethylethyl)-4H-selenopyrylium] grouping, andR¹, R², R³ and R⁴ are each a hydrogen atom, namely a4-[[2-amino-3-[[2,6-bis-[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]selenopyryliumsalt;

k. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping,Q² is a 4-[2,6-bis(1,1-dimethylethyl)-4H-selenopyrylium] grouping, R³ isa propyl group, and R¹, R² and R⁴ are each a hydrogen atom, namely a4-[[2-propylamino-3-[[2,6-bis[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]selenopyryliumsalt;

l. Q¹ is a 2-(1,1-dimethylethyl)-6-methoxybenz[b]-4H-thiopyran-4-ylidenegrouping, Q² is a4-[2-(1,1-dimethylethyl)-6-methoxybenz[b]-4H-thiopyrylium] grouping, R¹,R² and R⁴ are each a hydrogen atom, and R³ is a but-2-yl group, namely,a4-[[3-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4Hthiopyran-4-ylidene]methyl]-4-oxo-2-[propylamino]-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]-6-methoxybenz[b]thiopyryliumsalt;

m. Q¹ is a6-[but-2-oxy]-2-(1,1-dimethylethyl)benz[b]-4H-thiopyran-4-ylidenegrouping, Q² is a4-[2-(1,1-dimethylethyl)-6-[but-2-oxy]benz[b]-4H-thiopyrylium] grouping,R¹, R² and R⁴ are each a hydrogen atom, and R³ is a propyl group,namely, a6-[but-2-oxy]-4-[[3-[[6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-thiopyran-4-ylidene]-methyl]-4-oxo-2-[propylamino]-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]benz[b]thiopyryliumsalt; and

n. Q¹ is a6-[but-2-oxy]-2-(1,1-dimethylethyl)benz[b]-4H-thiopyran-4-ylidenegrouping, Q² is a4-[6-[but-2-oxy]-2-(1,1-dimethylethyl)benz[b]-4H-pyrylium] grouping, R¹,R² and R⁴ are each a hydrogen atom, and R³ is a propyl group, namely a6-[but-2-oxy]-4-[[2-[propylamino]-3-[[6-[but-2-oxy]2-[1,1-dimethylethyl]-benz[b]-4H-thiopyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]benz[b]pyryliumsalt.

Correspondingly, specific preferred squaric acid derivatives of FormulaII are those in which:

a. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,and R¹, R³ and R⁴ are each a hydrogen atom, namely3-amino-4-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione;

b. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,R¹ is a hydrogen atom, and R³ and R⁴ are each an ethyl group, namely3-diethylamino-4-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione;

c. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,R³ is a butyl group and R¹ and R⁴ are each a hydrogen atom, namely3-butylamino-4-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione;

d. Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,R³ is a --CH₂ CH₂ SO₃ H grouping, and R¹ and R⁴ are each a hydrogenatom, namely2-(3-sulfonatoprop-1-ylamino)-4-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione;

e. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping,and R¹, R³ and R⁴ are each a hydrogen atom, namely3-amino-4-[[2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione;

f. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping,R¹ is a methyl group, and R³ and R⁴ are each a hydrogen atom, namely3-amino-4-[1-[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]eth-1-yl]cyclobut-3-ene-1,2-dione;

g. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping,R¹ is a methyl group, R³ is a butyl group and R⁴ is a hydrogen atom,namely3-butylamino-4-[1-[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]-eth-1-yl]cyclobut-3-ene-1,2-dione;

h. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping,and R¹, R³ and R⁴ are each a hydrogen atom, namely3-amino-4-[[2,6-bis-[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione;

i. Q¹ is a 2,6-bis(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping,R³ is a propyl group, and R¹ and R⁴ are each a hydrogen atom, namely3-n-propylamino-4-[[2,6-bis[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]-methyl]-cyclobut-3-ene-1,2-dione;

j. Q¹ is a2-(1,1-dimethylethyl)-6-[but-2-oxy]benz[b]-4H-thiopyran-4-ylidenegrouping, R³ is is a propyl group, and R¹ and R⁴ are each a hydrogenatom, namely4-[[2-[1,1-dimethylethyl]-6-[but-2-oxy]benz[b]-4H-thiopyran-4-ylidene]methyl]-3-propylaminocyclobut-3-ene-1,2-dione;and

k. Q¹ is a 2-(1,1-dimethylethyl)-6-[but-2-oxy]benz[b]-4H-pyran-4-ylidenegrouping, R³ is is a propyl group, and R¹ and R⁴ are each a hydrogenatom, namely4-[[2-[1,1-dimethylethyl]-6-[but-2-oxy]benz[b]-4H-pyran-4-ylidene]methyl]-3-propylaminocyclobut-3-ene-1,2-dione.

The dyes produced by the processes of the present invention may be usedin any of the applications in which prior art near infra-red absorbershave been used. Thus, the dyes may be used as dyes in printing inksintended to provide markings which can be read under near infra-redradiation, for example, on packages of container items intended to bescanned by near infra-red laser scanners. At least some of the presentdyes may also be useful as charge transfer materials for use inxerography, electrophotography and similar processes, and as laser dyes.

However, because of their high extinction coefficients in the nearinfra-red region, the dyes produced by the present processes areespecially useful in processes for generating heat in a medium; in sucha process at least part of the medium is exposed to near infra-redactinic radiation of a frequency absorbed by the dye, so that theradiation is absorbed by the dye and heat is generated within the partsof the medium exposed to the radiation. Typically, in such a process,the radiation is provided by a laser. The medium may also comprise athermally sensitive material capable of undergoing a color change uponexposure to heat; the medium is exposed imagewise to the radiation, andthe heat generated by the dye is sufficient to effect a color change inthe thermally sensitive material, so that an image is formed in themedium. Thus, for example, the present dyes may be used as the nearinfra-red absorbers in the thermal imaging processes described in U.S.Pat. Nos. 4,602,263 and 4,826,976, and in the aforementioned copendingapplications U.S. Ser. Nos. 07/695,641; 07/696,196 and 07/695,932. Theseimaging processes rely upon the irreversible unimolecular fragmentationof one or more thermally unstable carbamate moieties of an organiccompound to effect a visually discernible color shift from colorless tocolored, from colored to colorless or from one color to another.

In such a process, preferably the thermally sensitive material isoriginally substantially colorless and is converted by the heatgenerated to a colored material in exposed areas of the image.Multi-colored images may be produced using a heat-sensitive elementcontaining an imaging layer of colorless imaging compound (leuco dye)for forming a yellow image, an imaging layer of colorless imagingcompound for forming a cyan image, and an imaging layer of colorlessimaging compound for forming a magenta image. Preferred leuco dyes, andprocesses for their preparation, are described in U.S. Pat. No.4,663,518, and other preferred yellow-forming leuco dyes are describedin application U.S. Ser. No. 07/548,223, filed Jun. 29, 1990.

In the production of such multi-color images, each imaging layercontains, in addition to the leuco dye, an infra-red absorber selectedsuch that the three infra-red absorbers absorb radiation at differentpredetermined wavelengths above 700 nm sufficiently separated so thateach imaging layer may be exposed separately and independently of theothers by using infra-red radiation at the particular wavelengthsselectively absorbed by the respective infra-red absorbers. As anillustration, the yellow, magenta and cyan precursors may have infra-redabsorbers associated therewith that absorb radiation at (say) 760 nm,820 nm and 880 nm, respectively, and may be addressed by laser sources,for example, infra-red laser diodes emitting radiation at theserespective wavelengths so that the three imaging layers can be exposedindependently of one another. While each layer may be exposed in aseparate scan, it is usually preferred to expose all of the imaginglayers simultaneously in a single scan using multiple laser sources ofthe appropriate wavelengths. Instead of using superimposed imaginglayers, the heat-sensitive compounds and associated infra-red absorbersmay be arranged in an array of side-by-side dots or stripes in a singlerecording layer.

The dyes of the present invention may also be used in theacid-generating imaging process described in copending application Ser.No. 07/965,161 of Stephen J. Telfer, filed Oct. 23, 1992 (now U.S. Pat.No. 5,286,612).

A preferred thermal imaging medium of this invention will now bedescribed, though by way of illustration only, with reference to FIG. 6of the accompanying drawings, which is a schematic cross-section throughthe imaging medium. The thicknesses of the various layers shown in thedrawing are not to scale.

The imaging medium (generally designated 10) shown in FIG. 6 is intendedfor use in the production of transparencies and comprises asubstantially transparent support 12 formed of 4 mil (101 μm)poly(ethylene terephthalate) (PET) film incorporating an ultra-violetabsorber. Appropriate PET films are readily available commercially, forexample as P4C1A film from DuPont de Nemours., Wilmington, Del.

The imaging medium 10 also comprises a diffusion-reducing subcoat 14approximately 1 μm thick formed from a 10:1 w/w mixture of awater-dispersible styrene acrylic polymer (Joncryl 538 sold by S.C.Johnson & Son, Inc., Racine, Wis. 53403) and a water-soluble acrylicpolymer (Carboset 526 sold by The B.F. Goodrich Co., Akron, Ohio 44313).The presence of the minor proportion of water-soluble acrylic polymerreduces the tendency for the layer 14 to crack during the coatingprocess. The diffusion-reducing subcoat 14, which has a glass transitiontemperature of approximately 55° C., serves the function of aconventional subcoat, namely increasing the adhesion of the imaginglayer 16 (described in detail below) to the support 12. The subcoat 14also serves to reduce or eliminate migration of dye compound from theimaging layer 16 after imaging; if a conventional subcoat were employedin place of the diffusion-reducing subcoat 14, diffusion of the dyecompound from the layer 16 into the subcoat after imaging might causeloss of sharpness of the image. The subcoat 14 is coated onto thesupport 12 from an aqueous medium containing the water-dispersible andwater-soluble polymers.

A yellow imaging layer 16 is in contact with the diffusion-reducingsubcoat 14. This imaging layer 16 is approximately 5 μm thick andcomprises approximately 47.5 parts by weight of a leuco dye of theformula: ##STR8## in which R' is a tertiary butyl group (the compoundsin which R' is an isobutyl or benzyl group may alternatively be used),1.6 parts by weight of an infra-red dye of the formula: ##STR9## (whichmay be produced in a manner exactly analogous to the reaction of Example33 substituting the 6-[2-butoxy] salt for the 6-methoxy salt used inthat Example), 3.3 parts by weight of a hindered amine stabilizer(HALS-63, sold by Fairmount Chemical Co.), and 47.5 parts by weight of apoly(methyl methacrylate) binder (Elvacite 2021, sold by DuPont deNemours, Wilmington, Del.; this material is stated by the manufacturerto be a methyl methacrylate/ethyl acrylate copolymer, but its glasstransition temperature approximates that of poly(methyl methacrylate)).This binder has a glass transition temperature of approximately 110° C.The imaging layer 16 is applied by coating from a mixture of heptanesand methyl ethyl ketone.

(Alternatively, the infra-red dye of Formula IR1 above may be replacedby an infra-red dye of the formula: ##STR10## which may be prepared asdescribed in the aforementioned U.S. Pat. No. 5,405,976; essentially,this dye is produced by condensing two moles of a2-(1,1-dimethylethyl)-5,7-dimethoxy-4-methylbenzpyrylium salt with acroconate salt.

Superposed on the yellow imaging layer 16 is a diffusion-reducing layer18, which, like the first diffusion-reducing layer 14, serves to preventmigration of dye compound from the yellow imaging layer 16 on storageafter imaging. The diffusion-reducing layer 18, which is approximately 2μm thick, is formed of a water-dispersible styrene acrylic polymer(Joncryl 138 sold by S.C. Johnson & Son, Inc., Racine, Wis. 53403), andis coated from an aqueous dispersion. This layer has a glass transitiontemperature of approximately 60° C.

The next layer of the imaging medium 10 is a solvent-resistantinterlayer 20 approximately 4.6 μm thick and composed of a majorproportion of partially cross-linked polyurethane (NeoRez XR-9637polyurethane sold by ICI Resins US, Wilmington, Mass.) and a minorproportion of poly(vinyl alcohol) (Airvol 540, sold by Air Products andChemicals, Inc., Allentown, Pa. 18195). This solvent-resistantinterlayer 20 is coated from an aqueous dispersion. The interlayer 20not only helps to thermally insulate the imaging layers 14 and 22(described below) from one another during imaging, but also preventsdisruption and/or damage to the yellow imaging layer 16 and thediffusion-reducing layer 18 during coating of the magenta imaging layer22. Since the yellow imaging layer 16 and the magenta imaging layer 22are both coated from organic solution, if a solvent-resistant interlayerwere not provided on the layer 16 before the layer 22 was coated, theorganic solvent used to coat the layer 22 might disrupt, damage orextract leuco dye or infra-red absorber from the layer 16. Provision ofthe solvent-resistant interlayer 20, which is not dissolved by and doesnot swell in the organic solvent used to coat the layer 22, serves toprevent disruption of or damage to the layer 16 as the layer 22 iscoated. Furthermore, the solvent-resistant interlayer 20 serves toprevent the magenta leuco dye, infra-red dye and hindered amine lightstabilizer from the layer 22 sinking into the diffusion-reducing layer18 and the yellow imaging layer 16 as the layer 22 is being coated.

Superposed on the solvent-resistant interlayer 20 is the magenta imaginglayer 22, which is approximately 3 μm thick and comprises approximately47.25 parts by weight of a leuco dye of the formula: ##STR11## (thisleuco dye may be prepared by the methods described in U.S. Pat. Nos.4,720,449 and 4,960,901), approximately 3.4 parts by weight of zincacetate (thus giving a leuco dye: zinc cation molar ratio of about1:0.4), 1.62 parts by weight of an infra-red dye of the formula:##STR12## (which may be produced in a manner exactly analogous to thereaction of Example 27 substituting the 6-[2-butoxy] salt for the6-methoxy salt used in that Example), 3.6 parts by weight of a hinderedamine stabilizer (HALS-63), 0.27 parts by weight of a wetting agent, and47.25 parts by weight of a polyurethane binder (Estane 5715, supplied byThe B.F. Goodrich Co., Akron, Ohio 44313). The imaging layer 22 isapplied by coating from a cyclohexanone/methyl ethyl ketone mixture.

Alternatively, the infra-red dye of Formula IR3 above may be replaced bythe dye of formula: ##STR13## (prepared in Example 22 below), or by thedye of formula: ##STR14## (prepared in Example 19 below).

On the imaging layer 22 is coated a second solvent-resistant interlayer24 which is formed from the same material, and coated in the same manneras, the solvent-resistant interlayer 20.

Superposed on the second solvent-resistant interlayer 24 is a cyanimaging layer 26, which is approximately 3 μm thick and comprisesapproximately 49.5 parts by weight of a leuco dye of the formula:##STR15## (this leuco dye may be prepared by the methods described inthe aforementioned U.S. Pat. Nos. 4,720,449 and 4,960,901),approximately 3.97 grams of zinc acetate (thus giving a leuco dye: zinccation molar ratio of about 1:0.4), 1.62 parts by weight of an infra-reddye of the formula: ##STR16## (prepared in Example 25 below), 0.2 partsof a wetting agent, and 49.5 parts by weight of a polyurethane binder(Estane 5715). The imaging layer 26 is applied by coating from methylethyl ketone.

(Alternatively, the infra-red dye of Formula IR6 above may be replacedby the dye of formula: ##STR17## which is preferably prepared by theprocess described in the aforementioned copending application U.S. Ser.No. 07/696,222; essentially this process comprises reacting a diester,diacid chloride or monoester monoacid chloride of squaric acid with a2-(1,1-dimethylethyl)-7-diethylamino-4-methylbenzpyrylium salt andhydrolysing to produce a compound of the formula: ##STR18## and thenreacting this compound with a7-alkoxy-2-(1,1-dimethylethyl)-4-methylbenzpyrylium salt to give thefinal infra-red dye of Formula IR7.

As already indicated, the layers 14-26 of the imaging medium 10 areproduced by coating on to the transparent rapport 12. However, theremaining layers of the imaging medium 10, namely the transparentbubble-suppressant layer 32, the ultraviolet filter layer 30 and theadhesive layer 28 are not coated on to the layer 26 but rather areprepared as a separate unit and then laminated to the remaining layersof the medium.

The transparent bubble-suppressant layer 32 is a 1.75 mil (44 μm) PETfilm, a preferred film being that sold as ICI 505 film by ICI Americas,Inc., Wilmington, Del. The bubble-suppressant layer 32 prevents theformation of bubbles in the imaging layers 16, 22 and 26 of the imagingmedium 10 during imaging.

The ultraviolet filter layer 30 serves to protect the imaging layers 16,22 and 26 from the effects of ambient ultraviolet radiation. It has beenfound that the leuco dyes are susceptible to undergoing color changeswhen exposed to ultraviolet radiation during storage before or afterimaging; such color changes are obviously undesirable since theyincrease the D_(min) of the image and may distort the colors therein.The ultraviolet filter layer 30 is approximately 5 μm thick andcomprises approximately 83 percent by weight of a poly(methylmethacrylate) (Elvacite 2043, sold by DuPont de Nemours, Wilmington,Mass.), 16.6 percent by weight of an ultraviolet filter (Tinuvin 328sold by Ciba-Geigy, Ardsdale, N.Y.) and 0.4 percent by weight of awetting agent. The ultraviolet filter layer 30 is prepared by coating onto the bubble-suppressant layer 32 from a solution in methyl ethylketone.

The adhesive layer, which is approximately 2 μm thick, is formed of awater-dispersible styrene acrylic polymer (Joncryl 138 sold by S.C.Johnson & Son, Inc., Racine, Wis. 53403) and is coated on to theultraviolet filter layer 30 from an aqueous dispersion.

After the layers 30 and 28 have been coated on to the bubble-suppressantlayer 32, the entire structure containing these three layers islaminated under heat (approximately 225° F., 107° C.) and pressure tothe structure containing the layers 12-26 to form the complete imagingmedium 10.

If desired, the bubble-suppressant layer 32 may be formed by coating,rather than by lamination of a pre-formed film on to the layers 12-26.If the bubble-suppressant layer 32 is to be formed by coating, it isconvenient to incorporate an ultra-violet absorber into thebubble-suppressant layer, thereby avoiding the need for a separateultra-violet absorber layer. Thus, in this case, the layer 28 is coatedon to the layer 26 using the solvent already described, and then thebubble-suppressant layer 32 containing the ultra-violet absorber may becoated on to the layer 28 from an aqueous medium.

The medium 10 is imaged by exposing it simultaneously to the beams fromthree infra-red lasers having wavelengths of approximately 790, 850 and920 nm. The 920 nm beam images the yellow imaging layer 16, the 850 nmbeam images the magenta imaging layer 22 and the 790 nm beam images thecyan imaging layer 26. Thus, a multicolor image is formed in the imagingmedium 10, and this multicolor image requires no further developmentsteps. Furthermore, the medium 10 may be handled in normal room lightingprior to exposure, and the apparatus in which the imaging is performedneed not be light-tight.

Alternatively, the present dyes may be used in a thermal imaging processin which the medium comprises one layer of a multi-layer structure, thisstructure further comprising a support layer disposed on one side of themedium and a colored layer adhering to the opposed side of the medium.In this type of thermal imaging process, the heat generated on exposureof the dye to actinic radiation causes increased adhesion of the coloredlayer to the support layer, such that upon application of a peelingforce to the colored-layer, the colored layer will peel from the supportlayer in areas which have not been exposed to the radiation, but inareas which have been exposed to radiation the colored layer will remainattached to the support layer. A preferred thermal imaging process ofthis type is described and claimed in International Patent ApplicationNo. PCT/US87/03249 (Publication No. WO88/04237).

From the foregoing description, it will be seen that the presentinvention provides near infra-red dyes with enhanced compatibility witha variety of media and which can be arranged to have absorptions withinnarrow wavelength ranges. Furthermore, these dyes can contain a varietyof functional groups. The processes of the present invention enableasymmetric infra-red dyes of the invention to be synthesized without theneed to separate mixtures of asymmetric and symmetric dyes.

The following Examples are now given, though by way of illustrationonly, to show details of particularly preferred reagents, conditions andtechniques used in the processes of the present invention.

EXAMPLES 1-15 First Process of the Invention

The following Examples 1-15 illustrate the first process of theinvention, that is to say reactions analogous to reaction K→L, shown inFIG. 2, together with certain reactions used for the preparation of thenecessary starting materials, and conversion of compounds of Formula IIto other compounds of Formula II.

Example 1 Preparation of4-[[7-diethylamino-2-(1,1-dimethylethyl)benz[b]-4H-pyran-4-ylidene]methyl]-3-butoxycyclobut-3-ene-1,2-dione

This Example illustrates the preparation, by a reaction analogous toB+H→K shown in FIG. 1, of the squaric acid derivative K in which R¹ is ahydrogen atom.

A solution of 7-diethylamino-2-(1,1-dimethylethyl)-4-methylbenzpyryliumtetrafluoroborate (3.57 g, 10 mmol, prepared as described in theaforementioned copending application U.S. Ser. No. 07/616,639) indichloromethane (20 mL) was added dropwise over two hours to a solutionof dibutyl squarate (2.5 g, 11 mmol, available from Aldrich ChemicalCompany, Milwaukee, Wis.) and triethylamine (2.02 g, 20 mmol) indichloromethane (30 mL) at room temperature. After the addition had beencompleted, the reaction mixture was heated under reflux for three hours.The solvent was then removed and diethyl ether (50 mL) was added. Theether solution was filtered and the solid residue was washed with moreether (50 mL). The combined ether extracts were concentrated, and thecrude product thus obtained was purified by flash chromatography onsilica gel with 30% ether/hexanes as eluent to give4-[[7-diethylamino-2-(1,1-dimethylethyl)benz[b]-4H-pyran4-ylidene]methyl]-3-butoxycyclobut-3-ene-1,2-dioneas a red solid (1.35 g, 29% yield) which melted at 145°-146° C. Thestructure of this compound was confirmed by mass spectroscopy and by ¹ Hand ¹³ C NMR spectroscopy.

(The filtrate from the ether extraction was collected, dissolved indichloromethane, washed sequentially with 1M hydrochloric acid, asaturated solution of sodium hydrogen carbonate and brine, and driedover magnesium sulfate. Removal of solvent yielded3,4-bis[[7-diethylamino-2-(1,1-dimethylethyl)benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dioneas a green solid (1.14 g, 37% yield) which did not melt below 300° C.The structure of this compound was confirmed by mass spectroscopy and by¹ H and ¹³ C NMR spectroscopy.)

Examples 2-4 Preparation of squaric acid derivatives, analogues of thecompound prepared in Example 1

The following squaric acid derivatives, which differ from the derivativeprepared in Example 1 in the group R¹ and/or by replacement of thebenzpyrylium grouping with a thiopyrylium or selenopyrylium grouping,were prepared in the same manner as in Example 1.

Example 24-[[2,6-bis[1,1-dimethylethyl]thiopyran-4-ylidene]methyl]-3-butoxy-cyclobut-3-ene-1,2-dione

This is the compound of Formula III in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, R¹ is ahydrogen atom, and A is a butoxy group. The starting material used was2,6-bis[1,1-dimethylethyl]-4-methylthiopyrylium tetrafluoroborate, thepreparation of which is described in U.S. Pat. No. 4,343,948 toKawamura.

Example 34-[1-[2,6-bis[1,1-dimethylethyl]thiopyran-4-ylidene]eth-1-yl]-3-butoxycyclobut-3-ene-1,2-dione

This is the compound of Formula III in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, R¹ is amethyl group and A is a butoxy group. The starting material used was2,6-bis[1,1-dimethylethyl]-4-ethylthiopyrylium tetrafluoroborate.

Example 44-[[2,6-bis[1,1-dimethylethyl]selenopyran-4-ylidene]methyl]-3-butoxy-cyclobut-3-ene-1,2-dione

This is the compound of Formula III in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping, R¹ is ahydrogen atom, and A is a butoxy group. The starting material used was2,6-bis[1,1-dimethylethyl]-4-methylselenopyrylium tetrafluoroborate, thepreparation of which is described in the aforementioned copendingapplication U.S. Ser. No. 07/696,222.

Example 5 Preparation of3-amino-4-[[7-diethylamino-2-[1,1-dimethylethyl]-benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene_(r)1,2-dione

This Example illustrates the preparation, by the reaction KL shown inFIG. 2, of the aminosquaric acid derivative L in which R¹, R³ and R⁴ areeach a hydrogen atom, this derivative being the derivative of Formula IIin which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,and R¹, R³ and R⁴ are each a hydrogen atom.

A 30% solution of ammonium hydroxide (2 mL) was added to a solution of4-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-3-butoxycyclobut-3-ene-1,2-dione(300 mg, 0.71 mmol, prepared in Example 1 above) in tetrahydrofuran(THF, 10 mL) and the resultant mixture was stirred at room temperaturefor 3 hours. Dichloromethane and water were then added and the layerswere separated. Drying of the organic layer with magnesium sulfatefollowed by removal of the solvent afforded the desired product inessentially quantitative yield as a red solid which melted at 261°-264°C. The product was of sufficient purity to be used directly in the nextstep. The ¹³ C NMR spectrum of the product was: δ_(C) (75 MHz in d₆-DMSO) 189.1, 188.0, 180.1, 179.9, 166.7, 163.6, 154.3, 149.9, 137.6,124.8, 110.1, 108.8, 102.2, 97.1, 96.1, 43.7, 35.6, 27.8 and 12.4 ppm.The structure of this compound was also confirmed by mass spectroscopyand by ¹ H NMR spectroscopy of a sample prepared in an analogous,small-scale reaction.

Examples 6-8 Preparation of Aminosquaric Acid Derivatives

The following aminosquaric acid derivatives were prepared from thesquaric acid derivatives of Examples 2-4 respectively above using thesame reaction conditions as in Example 5 above.

Example 63-amino-4-[[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione

This is the compound of Formula II in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, and R¹, R³and R⁴ are each a hydrogen atom. The structure of this compound wasconfirmed by mass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy; the¹³ C spectrum was: δ_(C) (75 MHz in CDCl₃) 188.7, 188.3, 177.5, 168.1,156.8, 156.4, 145.6, 121.4, 120.9, 104.7, 38.9, 38.0, 30.5 and 30.3 ppm.

Example 73-amino-4-[1-[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]eth-1-yl]cyclobut-3-ene-1,2-dione

This is the compound of Formula II in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, R¹ is amethyl group, and R³ and R⁴ are each a hydrogen atom. The structure ofthis compound was confirmed by mass spectroscopy and by ¹ H and ¹³ C NMRspectroscopy; the ¹³ C spectrum was: δ_(C) (75 MHz in d₆ -DMSO) 192.1,190.0, 180.4, 169.5, 151.3, 146.9, 134.5, 120.0, 115.8, 112.2, 37.7,37.5, 29.9, 29.8 and 14.9 ppm.

Example 83-amino-4-[[2,6-bis-[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione

This is the compound of Formula II in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping, and R¹, R³and R⁴ are each a hydrogen atom. The structure of this compound wasconfirmed by mass spectroscopy and by ¹ H and ¹³ C NMR, spectroscopy;the ¹³ C spectrum was: δ_(C) (75 MHz in CDCl₃) 189.0, 188.7, 178.0,167.8, 159.7, 158.6, 146.1, 122.6, 121.8, 108.4, 40.0, 39.1, 31.0 and30.8 ppm.

Example 9 Preparation of3-diethylamino-4-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione

This Example illustrates the preparation, by the reaction KL shown inFIG. 2, of the aminosquaric acid derivative L in which R¹ is a hydrogenatom, and R³ and R⁴ are each an ethyl group, this derivative being thederivative of Formula II in which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,R¹ is a hydrogen atom, and R³ and R⁴ are each an ethyl group.

Diethylamine (20 mg, 0.27 mmol) was added to a solution of4-[[7-diethylamino-2-(1,1-dimethylethyl)benz[b]-4H-pyran-4-ylidene]methyl]-3-butoxycyclobut-3-ene-1,2-dione(80 mg, 0.19 mmol, prepared as in Example 1 above) in dichloromethane (1mL) and the resultant mixture was stirred at room temperature for 6hours. Removal of the solvent under reduced pressure afforded thedesired aminosquaric acid derivative, which was washed with ether togive a red solid (76 mg, 95% yield) which melted at 148°-150° C. Thestructure of this compound was confirmed by mass spectroscopy and by ¹ Hand ¹³ C NMR spectroscopy; the ¹³ C spectrum was:

δ_(C) (75 MHz in CDCl₃) 188.8, 187.9, 175.8, 166.0, 164.6, 155.0, 149.8,139.0, 124.1, 109.7, 109.5, 102.8, 97.8, 95.2, 44.5, 36.1, 28.0, 14.9and 12.6 ppm.

Examples 10-12 Preparation of Aminosquaric Acid Derivatives

The following aminosquaric acid derivatives were prepared using the samereaction conditions as in Example 9 above.

Example 103-butylamino-4-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione

This is the aminosquaric acid derivative L in which R³ is an n-butylgroup and R¹ and R⁴ are each a hydrogen atom, this derivative being thederivative of Formula II in which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,R³ is a butyl group and R¹ and R⁴ are each a hydrogen atom. It is onlynecessary to substitute an equimolar amount of butylamine for thediethylamine used in Example 9. The structure of this compound wasconfirmed by mass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy; the¹³ C spectrum was: δ_(C) (75 MHz in d₆ -DMSO) 188.5, 187.1, 177.7,165.5, 163.6, 154.3, 149.9, 137.7, 124.8, 110.1, 108.4, 102.2, 97.1,96.1, 54.9, 43.7, 43.5, 35.6, 32.6, 27.7, 19.1, 13.5 and 12.4 ppm.

Example 113-butylamino-4-[1-[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]eth-1-yl]cyclobut-3-ene-1,2-dione

This is the aminosquaric acid derivative of Formula II in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, R¹ is amethyl group, R³ is a butyl group and R⁴ is a hydrogen atom, and isobtained by replacing the starting material of Example 10 with thesquaric acid derivative prepared in Example 3 above. The structure ofthis compound was confirmed by mass spectroscopy and by ¹ H and ¹³ C NMRspectroscopy; the ¹³ C spectrum was:

δ_(C) (75 MHz in CDCl₃) 190.1, 189.8, 178.6, 170.0, 153.0, 150.9, 135.7,119.3, 116.0, 111.9, 45.1, 38.1, 33.3, 30.3, 19.6, 14.9 and 13.7 ppm.

Example 123-propylamino-4-[[2,6-bis[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]-methyl]cyclobut-3-ene-1,2-dione

This is the aminosquaric acid derivative of Formula II in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping, R³ is apropyl group, and R¹ and R⁴ are each a hydrogen atom. The startingmaterials used are propylamine and the squaric acid derivative preparedin Example 4 above. The structure of this compound was confirmed by massspectroscopy and by ¹ H NMR spectroscopy.

Example 13 Preparation of2-(3-sulfonatoeth-1-ylamino)-4-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione

This is the aminosquaric acid derivative L in which R³ is (notionally) a--CH₂ CH₂ SO₃ H grouping and R¹ and R⁴ are each a hydrogen atom, thisderivative being the derivative of Formula II in which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,R³ is (notionally) a --CH₂ CH₂ SO₃ H grouping, and R¹ and R⁴ are each ahydrogen atom.

4-[[7-Diethylamino-2-(1,1-dimethylethyl)benz[b]-4H-pyran-4-ylidene]methyl]-3-butoxycyclobut-3-ene-1,2-dione(155 mg, 0.36 mmol, prepared in Example 1 above), taurine (45 mg, 0.36mmol) and triethylamine (40 mg, 0.4 mmol) were stirred overnight at roomtemperature in water/diglyme (5 mL/10 mL). The mixture was thenconcentrated under reduced pressure, removing the water and some of thediglyme. Ether was added, and a solid residue was formed, which wasseparated and washed with more ether. The remaining material was thentreated with dichloromethane, which dissolved the desired product butnot excess taurine, which was removed by filtration. Removal ofdichloromethane gave orange crystals (80 mg) which were used in Example25 below without further purification. The structure of this compoundwas continued by mass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Example 14 Preparation of4-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene]methyl]-3-propylaminocyclobut-3-ene-1,2-dione

This Example illustrates the preparation, by reactions analogous to B+FJshown in FIG. 1 and JL (i.e., a reaction analogous to KL shown in FIG.2, but starting with the monoacid chloride rather than the monoester),of the aminosquaric acid derivative of Formula II in which Q¹ is a2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene grouping,R³ is an propyl group, and R² and R⁴ are each a hydrogen atom.

A solution of 2-[1,1-dimethylethyl]-6-methoxy-4-methylbenzthiopyryliumtetrafluoroborate (31.0 g, 93 mmol, prepared in Example 32 below) in drydimethylformamide (DMF, 200 mL) was added dropwise at room temperatureunder nitrogen to a solution of 3,4-dichlorocyclobut-3-ene-1,2-dione(15.7 g, 104 mmol, prepared as described in Schmidt, A. H, Synthesis,1980, 963) in dry DMF (200 mL) over a period of 5 hours. A red-browncolor developed. The reaction mixture was then cooled with an ice/waterbath, and propylamine (71.9 g, 1.22 mol) was added in a slow stream over10 minutes (a mildly exothermic reaction occurred). The dark red mixturewas then stirred at room temperature for 17 hours, after which it waspoured into a rapidly stirred mixture of ice/brine (1.5 L) andconcentrated hydrochloric acid (100 mL). The solid which separated wascollected by filtration, washed with water and air-dried to give thecrude product as a red-brown powder. Purification was effected bydissolving this material in dichloromethane (1 L) and slurrying withsilica gel (500 g of Selecto 142824 40 micron) for 10 minutes. Themixture was filtered, and the solid residue was washed withdichloromethane (10 100 mL aliquots). The solid residue was then setaside. The blue filtrate was treated in a similar manner with a further250 g of the silica gel, and the cycle of filtration and washing wasrepeated. The solid residue was combined with that set aside earlier,and the desired product was extracted from the silica gel by slurryingwith methanol for 10 minutes, followed by filtration. The filtrate wasreserved, and the silica gel was washed with more methanol (10 100 mLaliquots). The combined methanol extracts were concentrated underreduced pressure, and the resultant residue was dissolved indichloromethane (500 mL). Excess silica gel was removed by filtration,after which the solvent was removed under reduced pressure to give thepure aminosquarate derivative (21.17 g, 59.4% yield) as a brown powder.The structure of this compound was confirmed by mass spectroscopy and by¹ H and ¹³ C NMR spectroscopy.

Example 15 Preparation of4-[[6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-3-propylaminocyclobut-3-ene-1,2-dione

This Example illustrates the preparation, by reactions analogous tothose described in Example 14 above, of the aminosquaric acid derivativeof Formula II in which Q¹ is a6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene grouping,R³ is a propyl group, and R² and R⁴ are each a hydrogen atom.

Part A: Preparation of4-[[6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-3-chlorocyclobut-3-ene-1,2-dione

A solution of 6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (10.0 g, 27.8 mmol, prepared in Example 39, Part Cbelow) in acetonitrile (70 mL) was added dropwise over a period of 30minutes to a solution of 3,4-dichlorocyclobut-3-ene-1,2-dione (4.5 g,29.8 mmol, prepared as described in Schmidt, A. H., Synthesis, 1980,963) in a mixture of acetonitrile (10 mL) and N-methylpyrrolidone (NMP,20 mL), with ice/water cooling. A precipitate quickly formed, andstirring became somewhat difficult. The mixture was then allowed to warmto room temperature and stirring was continued for 1 hour, after whichthe mixture was refrigerated. The product was isolated by filtration,washed with a little cold acetonitrile, and air-dried to give a darkorange powder (6.71 g, 62% yield) which was pure enough for direct usein Part B below. The structure of this compound was confirmed by massspectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Part B: Preparation of4-[[6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-3-propylaminocyclobut-3-ene-1,2-dione

Propylamine (0.1 mL) was added to a stirred solution of4-[[6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-3-chlorocyclobut-3-ene-1,2-dione(2.27 g, 5.9 mmol, prepared in Part A above) in dichloromethane (40 mL)at room temperature, and the mixture was stirred for 17 hours at roomtemperature, during which time a precipitate formed. Hexanes (50 mL)were then added, and the precipitate was collected by filtration, washedwith 1:1 hexanes/dichloromethane (10 mL) and air dried to afford thedesired compound (2.3 g, 84% yield) as orange needles. Mass spectroscopyand ¹ H and ¹³ C NMR spectroscopy showed that the compound wasassociated with exactly one equivalent of propylamine, possibly in theform of a salt.

EXAMPLES 16-27 Second Process of the Invention

The following Examples 16-27 illustrate the second process of theinvention, that is to say reactions analogous to reaction L→A, shown inFIG. 2, together with certain reactions used for the conversion ofcompounds of Formula I to other compounds of Formula I.

Example 16 Preparation of4-[[2-amino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate

This Example illustrates the preparation, by the reaction L→A shown inFIG. 2, of the dye A in which R¹, R², R³ and R⁴ are each a hydrogenatom, this being the dye of Formula I in which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, and R¹, R², R³ and R⁴ are each a hydrogen atom.

A solution of the crude product from Example 5 above,7-diethylamino-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (prepared as described in the aforementioned copendingapplication U.S. Ser. No. 07/616,639, 250 mg, 0.7 mmol) and quinoline (5drops) was heated at reflux in butanol (5 mL) for 4 hours, then cooledand allowed to stand overnight. The crude product was separated byfiltration and washed with ether to afford green crystals of the dye(161 mg, 37% yield over the two steps of Example 5 and this Example)which had a principal infra-red absorption at 797 nm in dichloromethanesolution, ε=334,000. The structure of this compound was confirmed bymass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Examples 17-19 Preparation of Other Dyes

The following dyes were prepared from the aminosquaric acid derivativesof Examples 6-8 respectively above using the same reaction conditions asin Example 16 above.

Example 174-[[2-amino-3-[[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumtetrafluoroborate

This is the compound of Formula I in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping Q² is a4-[2,6-bis-(1,1-dimethylethyl)-4H-thiopyrylium] grouping, and R¹, R², R³and R⁴ are each a hydrogen atom. The dye had a principal infra-redabsorption at 805 nm in dichloromethane solution, ε=224,000. Thestructure of this compound was confirmed by mass spectroscopy and by ¹ HNMR spectroscopy.

Example 184-[[2-amino-3-[1-[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]eth-1-yl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumtetrafluoroborate

This is the compound of Formula I in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, Q² is a4-[2,6-bis-(1,1-dimethylethyl)-4H-thiopyrylium] grouping, R¹ is a methylgroup, and R², R³ and R⁴ are each a hydrogen atom. The structure of thiscompound was confirmed by mass spectroscopy. The impure unsymmetricaldye has a principal infra-red absorption at 834 nm in dichloromethanesolution.

Example 194-[[2-amino-3-[[2,6-bis[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]-selenopyryliumtetrafluoroborate

This is the compound of Formula I in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping, Q² is a4-[2,6-bis-(1,1-dimethylethyl)-4H-selenopyrylium] grouping, and R¹, R²,R³ and R⁴ are each a hydrogen atom. The dye had a principal infra-redabsorption at 844 nm in dichloromethane solution, ε=287,000. Thestructure of this compound was confirmed by mass spectroscopy and by ¹ Hand ¹³ C NMR spectroscopy.

Example 20 Preparation of4-[[3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-pivaloylamino-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate

This Example illustrates the preparation of the dye A in which R³ is apivaloyl grouping and R¹, R² and R⁴ are each a hydrogen atom (this beingthe dye of Formula I in which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ is a pivaloyl grouping and R¹, R² and R⁴ each a hydrogenatom), from the corresponding dye in which R³ is a hydrogen atom.

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU, 1 drop, available from theAldrich Chemical Company, Milwaukee, Wis.) was added to a mixture of4-[[2-amino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate (10 mg, 0.016 mmol, prepared in Example 16 above) andpivaloyl chloride (5 drops) in dichloromethane (2 mL). Dissolution ofthe dye starting material was observed over a period of 1 hour, afterwhich the crude reaction mixture was purified directly by preparativethin-layer chromatography on silica gel with 5% methanol/dichloromethaneas eluent to afford the desired dye (10 mg, 89% yield); this dye had aprincipal infra-red absorption at 782 nm in dichloromethane solution,ε=282,000. The structure of this dye was confirmed by ¹ H NMRspectroscopy and by mass spectroscopy.

Example 21 Preparation of4-[[3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl-4-oxo-2-[4-methylbenzene-1-sulfonyl]amino-2-cyclobuten-1-ylidene]methyl-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumhydroxide inner salt dye

This Example illustrates the preparation of the dye A (FIG. 2) in whichR³ is a toluenesulfonyl grouping and R¹, R² and R⁴ are each a hydrogenatom (this being the dye of Formula I in which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ is a toluenesulfonyl grouping and R¹, R² and R⁴ are each ahydrogen atom), from the corresponding dye in which R³ is a hydrogenatom.

A solution of DBU (12 mg 0.078 mmol in dichloromethane (0.5 mL) wasadded to a mixture of4-[[2-amino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl-4-oxo-2-cyclobuten-1-ylidene]methyl-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate (26 mg, 0.042 mmol, prepared in Example 16 above) andp-toluenesulfonyl chloride (14 mg, 0.073 mmol) in dichloromethane (5mL). The dark green suspension was converted to a dark brown solution,which was stirred at room temperature for 18 hours, after which timethin-layer chromatography indicated that the reaction was incomplete.More DBU (12 mg) and additional p-toluenesulfonyl chloride were addedand stirring was resumed at room temperature and continued for a further15 days. The reaction was found to be still incomplete at this point,and some undissolved material was present, so dimethylsulfoxide (2 mL)was added and the resultant solution was stirred at room temperature forone day. The reaction mixture was then worked up by pouring it into 1Mhydrochloric acid and extracting the resultant mixture withdichloromethane. The organic layer was dried over magnesium sulfate andconcentrated under reduced pressure to yield a residue which waspurified by preparative thin-layer chromatography with 2%methanol/dichloromethane as eluent to give the dye (6.1 mg, 19% yield)as a green solid; this dye had a principal infra-red absorption at 814nm in dichloromethane solution, ε=264,000. The structure of thiscompound was confirmed by mass spectroscopy and by ¹ H and ¹³ C NMRspectroscopy.

Example 22 Preparation of4-[[2-diethylamino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate

This Example illustrates the preparation, by the reaction L→A shown inFIG. 2, of the dye A in which R³ and R⁴ are each an ethyl group and R¹and R² are each a hydrogen atom, this being the dye of Formula I inwhich Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ and R⁴ are each an ethyl group and R¹ and R² are each ahydrogen atom.

A solution of the aminosquaric acid derivative prepared in Example 9above (70 mg, 0.17 mmol),7-diethylamino-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (61 mg, 0.17 mmol) and quinoline (22 mg, 0.17 mmol)was heated at reflux in butanol (5 mL) for 24 hours, after which timemore 7-diethylamino-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (60 mg, 0.17 mmol) was added, and reflux was resumedfor a further 8 hours. The reaction mixture was concentrated underreduced pressure, and the crude product was purified by flashchromatography on silica gel with 5% methanol/dichloromethane as eluent,followed by preparative thin-layer chromatography on silica gel with thesame eluent mixture. Dark red crystals (18 mg, 14% yield) were obtained.The dye had a principal infra-red absorption at 828 nm indichloromethane solution, ε=315,000. The structure of this compound wasconfirmed by mass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Examples 23 and 24 Preparation of Other Dyes

The following dyes were prepared from the indicated aminosquaric acidderivatives using the same reaction conditions as in Example 22 above.

Example 234-[[2-butylamino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]-pyryliumtetrafluoroborate

This is the dye A in which R³ is a butyl group and R¹, R² and R⁴ areeach a hydrogen atom, this being the dye of Formula I in which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ is a butyl group and R¹, R² and R⁴ are each a hydrogenatom. This dye, which was prepared simply by substituting theaminosquaric acid derivative prepared in Example 10 above in thereaction of Example 22, had a principal infra-red absorption at 810 nmin dichloromethane solution, and its structure was confirmed by massspectroscopy and by ¹ H NMR spectroscopy.

Example 244-[[2-propylamino-3-[[2,6-bis[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]selenopyrylium tetrafluoroborate

This is the dye of Formula I in which Q¹ is a2,6-bis-(1,1-dimethylethyl)-4H-selenopyran-4-ylidene grouping, Q² is a4-[2,6-bis(1,1-dimethylethyl)-4H-selenopyrylium] grouping, R³ is apropyl group, and R¹, R² and R⁴ are each a hydrogen atom. The startingmaterials used were the aminosquaric acid derivative prepared in Example12 above, and the selenopyrylium salt used as starting material inExample 4 above. The dye had a principal infra-red absorption at 860 nmin dichloromethane solution. The structure of this compound wasconfirmed by mass spectroscopy.

Example 25 Preparation of4-[[2-[3-sulfonatoeth-1-ylamino]-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliuminner salt dye

This Example illustrates the preparation, by the reaction L→A shown inFIG. 2, of the dye A in which R³ is (notionally) a --CH₂ CH₂ SO₃ Hgrouping, and R¹, R², and R⁴ are each a hydrogen atom, this being thedye of Formula I in which Q¹ is a2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyran-4-ylidene grouping,Q² is a 4-[2-(1,1-dimethylethyl)-7-diethylaminobenz[b]-4H-pyrylium]grouping, R³ is (notionally) a --CH₂ CH₂ SO₃ H grouping, and R¹, R² andR⁴ are each a hydrogen atom.

A solution of the orange material prepared in Example 13 above, (70 mg,0.13 mmol), 7-diethylamino-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (50 mg, 0.14 mmol) and quinoline (17 mg, 0.13 mmol)was heated at reflux in butanol (5 mL) for 5 hours, then cooled andallowed to stand overnight at 5° C. The crude product was separated byfiltration and washed with ether to afford red crystals of the dye (36mg, 38% yield) which had a principal infra-red absorption at 814 nm indichloromethane solution, ε=333,000. The structure of this dye wasconfirmed by mass spectroscopy and by ¹ H NMR spectroscopy.

Example 26 Preparation of6-[but-2-oxy]-4-[[3-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene]methyl]-4-oxo-2-[propylamino]-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate

This Example illustrates the preparation of the dye of Formula I inwhich Q¹ is a2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene groupingQ² is a 6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]pyrylium grouping, R³is a propyl group and R¹, R² and R⁴ are each a hydrogen atom. In thisExample, the aminosquaric acid derivative of Formula II contains thebenzthiopyrylium nucleus, and the reaction is promoted with a Lewisacid, namely titanium tetrachloride.

Titanium tetrachloride (8 mL of a 1M solution in dichloromethane, 8mmole) was added to a solution of4-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene]methyl]-3-propylaminocyclobut-3-ene-1,2-dione(1.0 g, 2.6 mmol, prepared in Example 14 above),6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (1.0 g, 2.8 mmole, prepared in Example 39 below) andquinoline (2.8 g, 22 mmole) in dichloromethane (150 mL) at roomtemperature under nitrogen, and the mixture was stirred at roomtemperature for 2 hours. The mixture was then washed sequentially with200 mL quantities of:

i) water containing tetrafluoroboric acid (10 mL of a 48% aqueoussolution);

ii) water;

iii) 10% aqueous sodium hydrogen carbonate solution;

iv) water; and

v) 10% aqueous sodium tetrafluoroborate solution.

The organic layer was then dried over anhydrous sodium sulfate andconcentrated. The residue was partially purified by flash chromatographyon silica gel with 0-2% methanol/dichloromethane as eluent. Furtherpurification was effected by stirring the chromatographed material withmethyl t-butyl ether (MTBE) (5 mL), storing the resultant suspension ina freezer (at about 5° C.) for 17 hours, removing the solvent bydecantation and triturating the residue with hexanes (25 mL). Air-dryingfollowing this purification afforded a brown powder, which stillcontained impurities. Final purification was achieved by stirring thebrown powder for 5 minutes in a mixture of acetone (5 mL) and hexanes(10 mL). The brown, suspended material was collected by filtration,washed with a further small amount of 1:2 acetone/hexanes, and air driedto afford the dye (0.47 g, 25% yield). The dye had an absorption in thenear infra-red in dichloromethane solution at 848 nm, ε=230,000. Thestructure of this compound was confirmed by mass spectroscopy and by ¹ Hand ¹³ C NMR spectroscopy.

Example 27 Preparation of6-[but-2-oxy]-4-[[3-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene]methyl]-4-oxo-2-[propylamino]-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate

This Example illustrates the preparation of the same dye as in Example26 above, but starting from an aminosquaric acid derivative of FormulaII containing the benzpyrylium nucleus. Again, the reaction is promotedwith a Lewis acid, namely titanium tetrachloride.

Titanium tetrachloride (3 mL of a 1M solution in dichloromethane, 3mmol) was added over a period of 30 seconds to a solution of6-[but-2-oxy]-4-[[2-1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-3-propylaminocyclobut-3-ene-1,2-dione(0.41 g, 1 mmol, prepared in Example 15 above),2-[1,1-dimethylethyl]-6-methoxy-4-methylbenzthiopyryliumtetrafluoroborate (0.36 g, 1.1 mmol, prepared in Example 32 below) andquinoline (1.1 g, 8.5 mmol) in dichloromethane (35 mL) at roomtemperature under nitrogen. The mixture was stirred at room temperaturefor 2 hours, then washed sequentially with 50 mL quantities of:

i) water containing tetrafluoroboric acid (2 mL of a 48% aqueoussolution);

ii) water;

iii) water containing sodium hydrogen carbonate (3 g);

iv) water; and

v) water containing sodium tetrafluoroborate (3 g).

The organic layer was then dried over anhydrous sodium sulfate andconcentrated. The residue was partially purified by trituration with 2:1hexanes/acetone (15 mL). Collection of the solid remaining aftertrituration by filtration, followed by washing with a further smallamount of 2:1 hexanes/acetone afforded the dye as a coppery powder (0.22g, 30% yield). This material was spectroscopically identical to thematerial prepared in Example 26 above.

EXAMPLE 28 Third Process of the Invention

The following Example 28 illustrates the third process of the invention,that is to say the preferred reaction for the preparation of thesulfonamide dyes of the invention.

Example 28 Preparation of4-[[3-[[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-butanesulfonylamino-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumhydroxide inner salt dye

This Example illustrates the preparation of a dye of Formula I, in whichQ¹ is a 2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, Q²is a 4-[2,6-bis(1,1-dimethylethyl)-4H-thiopyrylium] grouping, R³ is aCH₃ CH₂ CH₂ CH₂ SO₂ -- grouping, and R¹, R² and R⁴ are each a hydrogenatom, starting from the corresponding dye in which the squaryliumnucleus is unsubstituted.

Butanesulfonyl isocyanate (3 drops, approx. 30 mg) was added to asolution of4-[[3-[[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]thiopyryliumhydroxide inner salt dye (100 mg, 0.19 mmol, prepared as described inU.S. Pat. No. 4,508,811) in toluene (15 mL) and the reaction mixture washeated to 95° C. for 2 hours. Additional butanesulfonyl isocyanate (3drops) was added and heating was continued for a further 2 hours. Afinal addition of butanesulfonyl isocyanate (3 drops) then took place,followed by heating for 2 more hours. The reaction mixture was thendiluted with ether and washed with water. The organic layer was driedover sodium sulfate and concentrated under reduced pressure, then theresidual dark green oil produced was purified by flash chromatography onsilica gel. The material which eluted first from the column was the dye(3.4 mg, 3% yield) which had a principal infra-red absorption at 828 nmin dichloromethane solution. The structure of this compound wasconfirmed by ¹ H NMR spectroscopy and mass spectroscopy.

EXAMPLES 29-37 Fourth Process of the Invention

The following Examples 29-37 illustrate the fourth process of theinvention, that is to say reactions analogous to Q→R shown in FIG. 3,together with reactions analogous to P→Q shown in FIG. 3 and certainother reactions necessary for the preparation of starting materials.

Example 29 Preparation of 4-butylamino-3-ethoxycyclobut-3-ene-1,2-dione

This Example illustrates the preparation, by the reaction P→Q shown inFIG. 3, of the aminosquaric acid derivative Q in which R³ is a butylgroup and R⁴ is a hydrogen atom.

Butylamine (86 mg, 1.18 mmol) was added to a solution of diethylsquarate (200 mg, 1.18 mmol) in dichloromethane (5 mL) at roomtemperature, and the reaction mixture was stirred for one hour. Theslightly cloudy mixture was then filtered and evaporated to give thedesired aminosquaric acid derivative as a yellowish solid (216 mg, 93%yield). The structure of this compound was confirmed by massspectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Example 30 Preparation of4-[[2-butylamino-3-[[2,6-bis[1,1-dimethylethyl]thiopyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]thiopyryliumtetrafluoroborate

This Example illustrates the preparation, by the reaction Q+R→N shown inFIG. 3, of the dye Q in which R³ is a butyl group and R¹, R² and R⁴ areeach a hydrogen atom, this being the dye of Formula I in which Q¹ is a2,6-bis(1,1-dimethylethyl)-4H-thiopyran-4-ylidene grouping, Q² is a4-[2,6-bis(1,1-dimethylethyl)-4H-thiopyrylium] grouping, R³ is a butylgroup and R¹, R² and R⁴ are each a hydrogen atom.

4-Butylamino-3-ethoxycyclobut-3-ene-1,2-dione (prepared in Example 29above, 50 mg, 0.25 mmol),2,6-bis[1,1-dimethylethyl]-4-methylthiopyrylium tetrafluoroborate (seeU.S. Pat. No. 4,343,948, 155 mg, 0.5 mmol) and quinoline (150 mg, 1.18mmol) were heated at reflux in butanol (5 mL) for one hour. The reactionmixture was then held at room temperature overnight, after which it washeated at reflux for a further 2 hours. The solvent was removed underreduced pressure and the residue was triturated with ether. The etherextracts, which contained the dye, were concentrated and the crudematerial was partially purified by preparative thin-layer chromatographyon silica gel with 7% methanol/dichloromethane as eluent. Repeating thechromatographic purification gave the dye (3.2 mg, 2% yield) as a brownglass. The dye exhibited a principal infra-red absorption at 816 nm indichloromethane solution, ε=135,000. The structure of this dye wasconfirmed by mass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Examples 31-33 Preparation of4-[[3-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene]methyl]-4-oxo-2-[propylamino]-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]-6-methoxybenz[b]thiopyryliumtetrafluoroborate

These Examples illustrate the preparation of the dye of Formula I inwhich Q¹ is a2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene grouping,Q² is a 2-[1,1-dimethylethyl]-6-methoxybenz[b]-thiopyrylium grouping, R³is a propyl group and R¹, R² and R⁴ are each a hydrogen atom.

Example 31 Preparation of2-[butoxy]-4-[propylamino]cyclobut-3-ene-1,2-dione

This Example illustrates a reaction analogous to P→Q shown in FIG. 3,but which produces the butyl homologue of the compound P in which theNR³ R⁴ is a propylamino group.

A solution of propylamine (26 mL, 0.31 mmol) in ether (100 mL) was addedto a solution of dibutyl squarate (57.68 g, 0.255 mmol) in ether (300mL), and the mixture was allowed to stand at room temperature for twohours, then filtered and the filtrate concentrated under reducedpressure to yield a yellow, oily solid (52.46 g, 97.5% yield). Thestructure of this compound was confirmed by mass spectroscopy and by ¹ Hand ¹³ C spectroscopy.

Example 32 Preparation of2-[1,1-dimethylethyl]-6-methoxy-4-methylbenz[b]thiopyryliumtetrafluoroborate

This Example illustrates the preparation of the6-methoxy-7-unsubstituted thiopyrylium analogue of the compound M shownin FIG. 2 in which R² is a hydrogen atom (i.e., the 4-substituent is amethyl group).

Part A: Preparation of ethyl 4,4-dimethylpent-2-ynoate

This is an improved preparation of a compound described in E. A.Halohen, Acta Chem. Scand., 9, 1492-1497 (1955).

t-Butylacetylene (15.38 g, 0.188 mol) was dissolved in tetrahydrofuran(100 mL) in a 500 mL three-necked round-bottomed flask fitted with anitrogen bubbler, rubber septum and dropping funnel. The resultantsolution was cooled to -70° C. using a dry ice/acetone bath, and butyllithium (72 mL of a 2.5M solution in hexanes, 0.18 mol) was addeddropwise via a syringe. The cooling bath was then removed and thereaction mixture was stirred for 30 minutes, during which time thetemperature in the flask rose to 10°-15° C. The flask was then againcooled to -70° C. and a solution of ethyl chloroformate (19.5 g, 0.18mol) was added dropwise. The cooling bath was again removed, and thereaction mixture was stirred for 3 hours. Cold water (75 mL) was nextadded to quench the reaction, and the aqueous and organic phases wereseparated. The aqueous phase was extracted with THF (50 mL) and thecombined organic phases were washed with 0.1M hydrochloric acid (75 mL)and brine (100 mL), and dried over magnesium sulfate. Removal of thesolvent under reduced pressure afforded a pale yellow oil (28 g) whichwas distilled under reduced pressure to provide the propiolate ester(23.5 g, 85% yield) as a colorless liquid which boiled at 70°-75° C. at18-20 mm Hg. The structure of this compound was confirmed by massspectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Part B: Preparation of 4-dimethyl-3-(4-methoxyphenylthio)pent-2-enoicacid

This and the next step are modifications of the methods described in M.R. Detty and B. J. Murray, J. Am. Chem. Soc., 105, 883-890 (1983).

A solution of 4-methoxybenzene thiol (14.0 g, 0.1 mol) in methanol (25mL) was added in one portion to sodium methoxide (21.6 g of a 25%solution in methanol, 0.1 mol) with ice/water bath cooling. The flaskwas warmed to room temperature, stirred for 15 minutes, and then cooledagain using the ice/water bath. A solution of ethyl4,4-dimethylpent-2-ynoate (15.4 g, 0.1 mol, prepared in Part A above) inmethanol (25 mL) was next added in one portion. The reaction mixture waswarmed to room temperature, stirred for one hour, and then diluted withethanol (95%, 75 mL). Potassium hydroxide (30 mL of a 40% aqueoussolution) was added, and the resultant solution was heated to 50°-60° C.using a water bath, and stirred at this temperature for 2 hours. Themixture was then cooled to room temperature and diluted with cold water(circa 400 mL). The resultant cloudy suspension was extracted withcarbon tetrachloride (3×100 mL) and the aqueous layer was acidified withice-cold 6M hydrochloric acid (to about pH 3), whereupon a precipitateof the desired carboxylic add separated. The product was extracted withdichloromethane (3 100 mL aliquots), and the solution was dried overmagnesium sulfate. Removal of solvent under reduced pressure affordedthe acid (21.4 g, 80% yield) as a white solid. The structure of thiscompound was confirmed by mass spectroscopy and by ¹ H and ¹³ C NMRspectroscopy.

Part C: Preparation of2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-one

Methanesulfonic add (2.6 g, 27 mmol) was added to a suspension of4-dimethyl-3-(4-methoxyphenylthio)pent-2-enoic acid (6.72 g, 25 mmol,prepared in Part B above) in acetic anhydride (20 mL). The reactionflask was then stirred and heated with a pre-heated oil bath at 80°-85°C. for about 30 minutes, during which time the color of the reactionmixture changed from brown to deep green. The mixture was then cooledand the reaction was quenched by addition of crushed ice/water (50 g).The resultant mixture was stirred for 20 minutes, then extracted withhexanes (5 50 mL aliquots). The combined hexane extracts were washedwith a saturated aqueous solution of sodium hydrogen carbonate and withbrine, and dried over magnesium sulfate. Removal of solvent underreduced pressure afforded the thiochromone (5.74 g). ¹ H NMR indicatedthat the material was almost pure, so this material was used withoutfurther purification in the reaction of Part D below.

Part D: Preparation of2-[1,1-dimethylethyl]-6-methoxy-4-methylbenz[b]thiopyryliumtetrafluoroborate

Methyl magnesium bromide (50 mL of a 3M solution in ether, 0.15 mmol)was added to a solution of the crude thiochromone (20 g, prepared inPart C above) in THF (100 mL) with cooling to 10° C. The reactionmixture was then allowed to warm to room temperature and stirred for 6hours. The mixture was then added, with vigorous stirring, totetrafluoroboric acid (125 mL of a 50% aqueous solution) which had beendiluted with ice/water (600 mL). A yellow precipitate formed, which wascollected by vacuum filtration, washed thoroughly with hexanes and driedunder reduced pressure to yield the desired salt (18.5 g, 55% yield overthree steps from the 4-methoxybenzene thiol). The structure of thiscompound was confirmed by mass spectroscopy and by ¹ H and ¹³ C NMRspectroscopy.

Example 33 Preparation of4-[[3-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene]methyl]-4-oxo-2-[propylamino]-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]-6-methoxybenz[b]thiopyryliumtetrafluoroborate

A solution of 2-[butoxy]-4-[propylamino]-cyclobut-3-ene-1,2-dione (5.16g, 24.4 mmol, prepared in Example 31 above) in dichloromethane (100 mL)was placed in a 2 L, three-necked round-bottomed flask equipped with amechanical stirrer, under a nitrogen atmosphere. The flask was thencharged with a suspension of2-[1,1-dimethylethyl]-6-methoxy-4-methylbenzthiopyryliumtetrafluoroborate (8.17 g, 24.4 mmol, prepared in Example 32 above) indichloromethane (400 mL), followed by a solution of quinoline (25.1 g,0.2 mol) in dichloromethane (50 mL), and finally by a solution oftitanium tetrachloride (26.7 mL of a 1M solution in dichloromethane,added using a syringe); a somewhat exothermic reaction followed thefinal addition. The resultant reaction mixture was stirred for 17 hours,after which time tetrafluoroboric acid (150 mL of a 55% aqueoussolution) was added. After a further one hour's stirring, the mixturewas extracted with water (2 100 mL aliquots), and the dichloromethanelayer was washed with saturated sodium bicarbonate solution (2 100 mLaliquots) and saturated sodium tetrafluoroborate solution (2 100 mLaliquots), dried, and concentrated under reduced pressure. The crudematerial thus obtained was dissolved in dichloromethane (50 mL) andprecipitated with MTBE (400 mL). Repeating this procedure provided thedye as a red-brown solid (5.21 g, 61% yield). The dye exhibited a nearinfra-red absorption in dichloromethane solution at 902 nm, ε=218,000.The structure of this compound was confirmed by mass spectroscopy and by¹ H and ¹³ C NMR spectroscopy.

Examples 34 and 35 Preparation of4-[[2-[but-2-ylamino]-3-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]-6-methoxybenz[b]thiopyryliumtetrafluoroborate

These Examples illustrate the preparation of the dye of Formula I inwhich Q¹ is a2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene grouping,Q² is a 2-[1,1-dimethylethyl]-6-methoxybenz[b]thiopyrylium grouping, R³is an but-2-yl group and R¹, R² and R⁴ are each a hydrogen atom.

Example 34 Preparation of2-[butoxy]-4-[but-2-ylamino]-cyclobut-3-ene-1,2-dione

This Example illustrates a reaction analogous to P→Q shown in FIG. 3,but which produces the butyl homologue of the compound P in which theNR³ R⁴ is a but-2-ylamino group.

sec-Butylamine (8.89 g, 0.122 mol) was added dropwise to a solution ofdibutyl squarate (25.0 g, 0.11 mol) in ether (100 mL) under a nitrogenatmosphere, with ice bath cooling, over a period of 10 minutes. Theresultant yellow solution was stirred at room temperature for 16 hours,after which time the solvent was removed under reduced pressure.Trituration with hexanes yielded the desired amine as a waxy solid,which was dried under a stream of nitrogen to give 27.25 g of product(contaminated with a trace of butanol). The structure of this compoundwas confirmed by ¹ H and ¹³ C NMR spectroscopy.

Example 35 Preparation of4-[[2-[but-2-ylamino]-3-[[2-[1,1-dimethylethyl]-6-methoxybenz[b]-4H-thiopyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2-[1,1-dimethylethyl]-6-methoxybenz[b]thiopyryliumtetrafluoroborate

Titanium tetrachloride (30 mL of a 1M solution in dichloromethane, 0.03mol) was added, over a period of 5 minutes, at room temperature undernitrogen, to a solution of2-[1,1-dimethylethyl]-6-methoxy-4-methylbenz[b]thiopyryliumtetrafluoroborate (3.75 g, 0.0112 mol, prepared in Example 32 above),2-butoxy-4-[but-2-ylamino]-cyclobut-3-ene-1,2-dione (2.55 g, 0.0113 mol,prepared in Example 34 above) and quinoline (18.0 g, 0.14 mol) indichloromethane (250 mL). The resultant mixture was stirred for 4 hours,after which time tetrafluoroboric acid (50 mL of a 48% aqueous solution)was added, followed by water (100 mL). The layers were separated, andthe organic phase was washed successively with 100 mL portions of water,water (100 mL) containing sodium hydrogen carbonate (10 g), water, andwater (100 mL) containing sodium tetrafluoroborate (10 g). The washedorganic phase was then dried over sodium sulfate and concentrated underreduced pressure to give a black residue which was triturated with 20 mLof a 3:1 hexanes/acetone mixture at 0° C. The solid was collected,washed with a further small portion of the cold triturating solution,and dried to afford the dye (2.75 g, 69% yield) as a dark brown powder,having an absorption maximum in dichloromethane solution at 902 nm,ε=179,200. The structure of this compound was confirmed by massspectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Examples 36 and 37 Preparation of4-[[2-[but-2-ylamino]-3-[[6-[2-ethylbut-1-oxy]-2-phenylbenz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-6-[2-ethylbut-1-oxy]-2-phenylbenz[b]pyryliumtetrafluoroborate

These Examples illustrate the preparation of the dye of Formula I inwhich Q¹ is a 6-[2-ethylbut-1-oxy]-2-phenylbenz[b]-4H-pyran-4-ylidenegrouping, Q² is a 6-[2-ethylbut-1-oxy]-2-phenylbenz[b]pyrylium grouping,R³ is an but-2-yl group and R¹, R² and R⁴ are each a hydrogen atom.

Example 36 Preparation of6-[2-ethylbut-1-oxy]-4-methyl-2-phenylbenzpyrylium tetrafluoroborate

This Example illustrates the preparation of the2-phenyl-4-methyl-6-[2-ethylbut-1-oxy] 7-unsubstituted analogue of thebenzpyrylium salt B shown in FIG. 1.

Part A: Preparation of 6-hydroxy-2-phenylbenz-4H-pyran-4-one

Trifluoromethanesulfonic acid (20 mL) was added dropwise, with stirring,to a mixture of hydroquinone (3.3 g, 0.03 mol) and ethyl3-oxo-3-phenylpropanoate (6.3 g, 0.033 mol). The dark red resultantsolution was stirred at room temperature for 2 hours, then heated to 60°C. for a further 2 hours, cooled and poured slowly into water (250 mL).The mixture so formed was stirred, and the solid product whichprecipitated was collected by filtration, washed with water, andrecrystallized from methanol (250 mL) to yield the desired chromone ascream-colored platelets (4.2 g, 59% yield). The structure of thiscompound was confirmed by mass spectroscopy and by ¹ H and ¹³ C NMRspectroscopy.

Part B: Preparation of 6-[2-ethylbut-1-oxy]-2-phenylbenz-4H-pyran-4-one

A mixture of 6-hydroxy-2-phenylbenz-4H-pyran-4-one (1.2 g, 5 mmol,prepared in Part A above), 1-bromo-2-ethylbutane (1.03 g, 7.5 mmol),potassium carbonate (1.04 g, 7.5 mmol) and sodium iodide (0.75 g, 5mmol) in methyl ethyl ketone (MEK, 10 mL) was heated for 17 hours atreflux under nitrogen. At this point thin layer chromatography indicatedthat the reaction was incomplete, so a further quantity of1-bromo-2-ethylbutane (1.03 g, 7.5 mmol) was added, and heating wasresumed for a further 8 hours. To drive the reaction to completion, afinal quantity of 1-bromo-2-ethylbutane (1.03 g, 7.5 mmol) was thenadded, and heating was continued for another 17 hours. The reactionmixture was poured into water (250 mL), and the resultant mixture wasacidified using concentrated hydrochloric acid, causing an oil toseparate. The mixture was extracted with ether (2 50 mL aliquots), andthe organic layers were washed with water (150 mL), dried over sodiumsulfate, and concentrated under reduced pressure to yield the product asa yellowish oil which solidified when scratched (1.6 g). The slightlyimpure material, whose structure was confirmed by ¹ H and ¹³ C NMRspectroscopy, was used directly in Part C below.

Part C: Preparation of6-[2-ethylbut-1-oxy]-4-methyl-2-phenylbenzpyrylium tetrafluoroborate

Methyl magnesium bromide (2 mL of a 3M solution in ether, 6 mmol) wasadded to a solution of 6-[2-ethylbut-1-oxy]-2-phenylbenz-4H-pyran-4-one(0.75 g, 2.5 mmol, prepared in Part B above) in THF (7.5 mL) at roomtemperature. An exothermic reaction accompanied the addition. Thereaction mixture was allowed to stand at room temperature for 17 hours,and then poured into a stirred solution of tetrafluoroboric acid (7 mLof an 8M solution, diluted with ice/water (200 mL)). Much foaming wasobserved, and a yellow/green precipitate was formed. The solid materialwas collected by filtration, washed with water and air dried to affordthe desired salt (0.875 g, 92% yield) as a green powder. The structureof this compound was confirmed by mass spectroscopy and by ¹ H and ¹³ CNMR spectroscopy.

Example 37 Preparation of4-[[2-[but-2-ylamino]-3-[[6-[2-ethylbut-1-oxy]-2-phenylbenz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-6-[2-ethylbut-1-oxy]-2-phenylbenz[b]pyryliumtetrafluoroborate

Titanium tetrachloride (0.8 mL of a 1M solution in dichloromethane, 0.8mmol) was added dropwise via a syringe to a solution of6-[2-ethylbut-1-oxy]-4-methyl-2-phenylbenzpyrylium tetrafluoroborate(190 mg, 0.5 mmol, prepared in Example 36 above),2-butoxy-4-[but-2-ylamino]-cyclobut-3-ene-1-2-dione (112 mg, 0.5 mmol,prepared in Example 34 above) and quinoline (510 mg, 4 mmol) indichloromethane (5 mL) at room temperature under nitrogen. The darkolive-green solution was stirred for 20 minutes, after which timetetrafluoroboric acid (5 mL of an 8M solution) was added and thereaction mixture was stirred for a further 17 hours. Water (10 mL) wasthen added, the organic layer was separated, and the aqueous layer wasextracted with dichloromethane. The combined dichloromethane layers wereconcentrated under reduced pressure to give a dark green residue, whichwas stirred with acetone (5 mL) for 10 minutes, precipitating theproduct. The dye was collected by filtration and washed with acetone togive a dark green solid (126 mg, 58 yield). The dye exhibited a nearinfra-red absorption in dichloromethane solution at 856 nm, ε=201,200.The structure of this compound was further confirmed by massspectroscopy.

EXAMPLES 38 and 39

The following two Examples illustrate the fourth process of theinvention carried out with promotion by a Lewis acid.

Example 38 Preparation of4-[[2-amino-3-[[2,6-bis-[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]selenopyryliumtetrafluoroborate

This Example illustrates the preparation of the same dye as in Example19 above but using trimethylsilyl chloride as a Lewis acid promoter ofthe condensation which produces the final dye.

Part A: Preparation of 4-amino-3-[but-1-oxy]cyclobut-3-ene-1,2-dione

Ammonia gas was bubbled into a solution of dibutyl squarate (22.6 g, 100mmol) in ether (500 mL) contained in a 1 L three-necked, round-bottomedflask equipped with a mechanical stirrer and an acidic scrubber.Precipitation of product ceased after 3 hours, so the reaction washalted and the ether solution was filtered. The solid residue was washedwith ether and set aside. The filtrate was allowed to stand at roomtemperature for a further 3 hours, after which time more solid wasobserved to have been precipitated. This solid was collected byfiltration, washed with ether, and combined with the material set asidepreviously. Drying in vacuo afforded the product as a white solid (15.7g, 92.9% yield). The structure of this compound was confirmed by massspectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Part B: Preparation of4-[[2-amino-3-[[2,6-bis-[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]selenopyryliumtetrafluoroborate

Dichloromethane (100 mL), quinoline (12.9 g, 100 mmol), trimethylsilylchloride (5.44 g, 50 mmol) and 4-amino-3-butoxycyclobut-3-ene-1,2-dione(1.69 g, 10 mmol, prepared in Part A above) were added sequentially to a250 mL three-necked round-bottomed flask containing2,6-bis-[1,1-dimethylethyl]-4-methylselenopyrylium tetrafluoroborate(8.93 g, 25 mmol, prepared as described in the aforementioned copendingapplication Ser. No. 07/696,222) under a nitrogen atmosphere. Thereaction mixture was heated at reflux for 17 hours, then quenched into acold solution of tetrafluoroboric acid (20 mL, 48% aqueous solution).The organic layer was separated, washed with water (2 50 mL aliquots),and dried over anhydrous magnesium sulfate, then concentrated underreduced pressure to approximately 50 mL, and poured into a beakercontaining diethyl ether (500 mL). The resultant solid was filtered,rinsed with ether and dried in vacuo to afford 5.7 g of the crudeproduct as a dark brick-red solid. Fractional crystallization byaddition of t-butyl methyl ether slowly to a methylene chloride solutionof the crude product afforded the pure dye (3.89 g, 55% yield), whichwas identical in all respects to material prepared as described inExample 19 above.

Example 39 Preparation of4-[[2-amino-3-[[6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate

This example illustrates the preparation of the dye of Formula I inwhich Q¹ is a6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene grouping,Q² is a 6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]pyrylium grouping, andR¹, R², R³ and R⁴ are each a hydrogen atom.

Part A: Preparation of2-[1,1-dimethylethyl]-6-hydroxybenz-4H-pyran-4-one

Trifluoromethanesulfonic acid (150 g) was added in a slow stream over aperiod of 30 minutes to a mixture of hydroquinone (30.0 g, 0.272 mol)and methyl 4,4-dimethyl-3-oxopentanoate (48.0 g, 0.304 mol) withice/water cooling to control the mildly exothermic reaction whichensued. The reaction mixture was then warmed to 50°-55° C. and held atthat temperature for 3 hours, during which time a red solution developedand, later, some solid material separated. The reaction mixture was thencooled and poured into stirred ice/water (1500 mL) containing saturatedbrine (100 mL), whereupon a gum separated, which solidified withscratching. This material was collected by filtration, washed with waterand air-dried to give the desired compound as a pale yellow powder (46.7g, 79% yield). The structure of this compound was confirmed by massspectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Part B: Preparation of6-[but-2-oxy]-2-[1,1-dimethylethyl]benz-4H-pyran-4-one

A mixture of 2-[1,1-dimethylethyl]-6-hydroxybenz-4H-pyran-4-one (25.0 g,0.115 mol, prepared in Part A above), 2-bromobutane (25.95 g, 0.189mol), potassium carbonate (50.0 g, 0.36 mol) and potassium iodide (20.0g, 0.12 mol) in MEK (250 mL) was stirred and heated at reflux undernitrogen for 8 hours. A further quantity of 2-bromobutane (8.65 g, 0.063mol) was then added, and heating was continued for another 16 hours. Themixture was cooled and poured into stirred ice/water (1000 mL) and themixture so formed was extracted with dichloromethane (2 400 mLaliquots). The combined organic extracts were washed with water (200 mL)and brine (200 mL), dried over magnesium sulfate and concentrated underreduced pressure to give the desired compound as a viscous, golden-brownoil (27.98 g, 89% yield). The structure of this compound was confirmedby mass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Part C: Preparation of6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate

Methyl magnesium bromide (100 mL of a 3M solution in ether, 0.3 mol) wasadded over a period of 20 minutes to a solution of6-[but-2-oxy]-2-[1,1-dimethylethyl]benz-4H-pyran-4-one (27.22 g, 0.099mol, prepared in Part B above) in dry THF (250 mL) maintained below 10°C. with an ice/water bath; some solid material was observed to separatefrom the yellow-brown solution. The ice bath was removed, and thereaction mixture was stirred at room temperature for 16 hours. Themixture was then poured cautiously into a rapidly stirred solution oftetrafluoroboric acid (90 mL of a 48% aqueous solution) in ice/water(1000 mL). Vigorous effervescence was observed, and the precipitatewhich formed was collected by filtration, washed with water, andair-dried to yield the salt as a pale yellow powder (30.08 g, 84%yield). The structure of this compound was confirmed by massspectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Part D: Preparation of4-[[2-amino-3-[[6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate

A solution of 6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (180 mg, 0.5 mmol, prepared in Part C above),4-amino-3-butoxycyclobut-3-ene-1,2-dione (43 mg, 0.25 mmol, prepared inExample 38, Part A above), quinoline (762 mg, 6 mmol), andtrimethylsilyl chloride (325 mg, 3 mmol) in dichloromethane (5 mL) washeated at reflux for 17 hours. The reaction mixture was then cooled toroom temperature, and tetrafluoroboric acid (5 mL of a 48% aqueoussolution) was added. Following this addition, the mixture was stirredrapidly for 30 minutes, during which time a precipitate formed. Theprecipitate was removed by filtration and reserved, while the filtratewas extracted with dichloromethane (2 25 mL aliquots). The combinedorganic layers were washed with water (25 mL) and concentrated underreduced pressure to yield a residue which was combined with theprecipitate reserved earlier. Acetone (5 mL) was added to this combinedcrude material, and the resultant suspension was stirred for 17 hours.The solid material remaining was collected by filtration, washed withacetone, and air-dried to afford the dye (75 mg, 42% yield) as copperycrystals. The dye exhibited a near infra-red absorption indichloromethane solution at 782 nm, ε=319,000. The structure of thiscompound was further confirmed by mass spectroscopy.

EXAMPLES 40-43 Fifth Process of the Invention

The following Examples 40-43 illustrate the fifth process of theinvention, that is to say reactions analogous to T→U shown in FIG. 4,together with a reaction analogous to S→T shown in FIG. 4.

Example 40 Preparation of6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylidenebenz[b]4H-pyran

This Example illustrates the reaction T→U shown in FIG. 4 carried out bymeans of a Peterson olefination.

Trimethylsilylmethylmagnesium chloride (5 mL of a 1M in ether, 5 mmol)was added to a solution of6-[but-2-oxy]-2-[1,1-dimethylethyl]benz-4H-pyran-4-one (1.37 g, 5 mmol,prepared in Example 39, Part B above) in anhydrous THF (10 mL) under anitrogen atmosphere, and the solution was heated to reflux for 3 hours.Thin layer chromatography of an aliquot indicated that the reaction wasnot complete, so an additional mount of trimethylsilylmethylmagnesiumchloride (5 mL of a 1M in ether, 5 mmol) was added and the reactionsolution was heated at reflux for a further 17 hours. An aqueoussolution of sodium hydroxide was then added, and the mixture was heatedat reflux for a further 1 hour, cooled, and filtered through a shortplug of Celite (manufactured by Johns-Manville Corporation, Denver,Colo. 80217). The upper, organic layer was separated, dried overanhydrous magnesium sulfate and concentrated to afford the crude productas a light yellow oil (1.05 g, 77% yield). The structure of thiscompound was confirmed by mass spectroscopy and by ¹ H and ¹³ C NMRspectroscopy.

Example 41 Preparation of6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylidenebenz[b]-4H-pyran

This Example illustrates the same reaction as in Example 40 above, butcarried out by use of a strong base on the corresponding 4-methyl salt.

Part A: Using Potassium t-butoxide

A solution of potassium t-butoxide (1 mL of a 1.0M solution in2-methyl-2-propanol, 1 mmol) was added dropwise to a suspension of6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (0.36 g, 1 mmol, prepared in Example 39, Part C above)in heptanes (10 mL) under a nitrogen atmosphere. The green suspensionwas converted to a brown solution after stirring at room temperature for30 minutes. The reaction mixture was stirred for an additional 30minutes, then poured into ice/water. The organic layer was separated,dried over anhydrous magnesium sulfate and concentrated under reducedpressure to afford the product as a brown oil (0.27 g, 100% yield). Thismaterial was spectroscopically identical to that prepared in Example 40above.

Part B: Using Potassium Hydride

A small amount of dry heptanes was added to a dispersion of potassiumhydride in mineral oil. The resultant suspension was centrifuged and theupper layer was decanted to give a gray solid. This solid was dried invacuo to afford 0.16 g of potassium hydride, which was then placed undera nitrogen atmosphere. Dry heptanes (10 mL) and6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylbenzpyryliumtetrafluoroborate (1.44 g, 4 mmol, prepared in Example 39, Part C above)were then added sequentially at room temperature. The solid suspensiondissolved within one hour. After stirring at room temperature for anadditional 1 hour, the solution was poured into ice/water, and theorganic layer was separated, dried over anhydrous magnesium sulfate andconcentrated under reduced pressure to afford the desired product as abrown oil (0.9 g, 82.5% yield). This material was spectroscopicallyidentical to that prepared in Example 40 above.

Example 42 Preparation of3-amino-4-[[6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione

This Example illustrates the reaction T→U shown in FIG. 4; the productis the aminosquaric acid derivative of Formula II in which Q¹ is a6-[but-2-oxy]-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene grouping,and R¹, R³ and R⁴ are each a hydrogen atom. The reaction is promotedwith a Lewis acid, namely aluminum chloride.

Aluminum chloride (0.66 g, 5 mmol) was added in one portion to asuspension of 4-amino-3-[but-1-oxy]cyclobut-3-ene-1,2-dione (0.676 g, 4mmol, prepared in Example 38, Part A above) in THF (20 mL) under anitrogen atmosphere. A light brown solution was obtained, together witha small amount of undissolved solid. A solution of6-[but-2-oxy]-2-[1,1-dimethylethyl]-4-methylidenebenz[b]-4H-pyran (1.05g, 3.86 mmol, prepared as described in Examples 40 and 41 above) in THF(10 mL) was then added slowly to the reaction mixture. A color change togreen was observed immediately. An additional amount of aluminumchloride (1 g, 7.5 mmol) was then added, followed by dropwise additionof pempidine (12 drops overall). The resultant red reaction solution wasstirred at room temperature for 17 hours, then quenched into ice/water.Addition of heptanes to the resultant mixture precipitated the desiredproduct, which was collected by filtration, rinsed with heptanes anddried in vacuo to afford the aminosquaric acid derivative (130 mg, 9.2%yield). The structure of this compound was confirmed by massspectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Example 43 Preparation of3-amino-4-[[2,6-bis-[1,1-dimethylethyl]seleno-4H-pyran-4-ylidene]methyl]cyclobut-3-ene-1,2-dione

This Example illustrates reactions analogous to S→T→U shown in FIG. 4but in which the starting material is the seleno analogue of the salt Rshown in FIG. 2, in which R¹ is a hydrogen atom. Thus, the product isthe same compound of Formula II prepared in Example 8 above.

A solution of potassium t-butoxide (1 mL of a 1.0M solution in2-methyl-2-propanol, 1 mmol) was added dropwise to a suspension of2,6-bis-[1,1-dimethylethyl]-4-methylselenopyrylium tetrafluoroborate(0.36 g, 1 mmol, prepared as described in copending application U.S.Ser. No. 07/696,222) in heptanes (10 mL) under a nitrogen atmosphere.The brown solid suspension was converted to a clear solution afterstirring at room temperature for 30 minutes. The reaction mixture wasstirred for an additional 30 minutes, then poured into ice/water. Theorganic layer was separated, dried over anhydrous magnesium sulfate andconcentrated under reduced pressure to afford 0.27 g of a reddish-brownoil.

A solution of this brown oil in THF (14 mL) was added dropwise to asuspension of 4-amino-3-[but-1-oxy]cyclobut-3-ene-1,2-dione (0.114 g, 1mmol, prepared in Example 38 above) and aluminum chloride (132 mg, 1mmol) in THF (10 mL) under a nitrogen atmosphere. A red solution formedimmediately after the addition. After stirring at room temperature for17 hours, the reaction solution was quenched into ice/water. The organiclayer was separated, dried over anhydrous magnesium sulfate, andconcentrated under reduced pressure to afford an impure product. Thisproduct was purified by preparative thin-layer chromatography on silicagel with 10% methanol/dichloromethane as eluent to afford the desiredproduct (30 mg, 9% yield). The structure of this compound was confirmedby mass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

EXAMPLES 44-53 Sixth Process of the Invention

The following Examples 44-53 illustrate the sixth process of theinvention, that is to say reactions analogous to V→W and W→X shown inFIG. 5.

Example 44 Preparation of4-[[2-butylamino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumtetrafluoroborate

This Example illustrates the reactions V→W and W→X shown in FIG. 5.

Part A: Preparation of4-[[3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-2-methoxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]-pyryliummethosulfate

Dimethyl sulfate (2.0 g, 15.8 mmol) was added to a solution of4-[[3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliumhydroxide inner salt dye (1.0 g, 1.6 mmol, prepared as described in theaforementioned copending applications Ser. Nos. 07/616,639 and07/795,038) in dichloromethane (50 mL) and the solution was stirred atreflux. Thin layer chromatography on silica gel with 10%methanol/dichloromethane as eluent indicated that trace amounts ofstarting material remained (R_(f) 0.9) after 24 hours' reflux, and thata substantial quantity of the desired methylated dye had been formed(R_(f) 0.7). The reaction mixture was accordingly worked up by washingwith water (3 50 mL aliquots) and drying over anhydrous sodium sulfate,after which the solution was concentrated under reduced pressure to avolume of about 5 mL. Methyl t-butyl ether (MTBE) (15 mL) was then addedto precipitate the product, which was collected by filtration, washedwith MTBE and dried to afford the methylated product (1.0 g, 83% yield).This material exhibited an infra-red absorption at 786 nm indichloromethane, ε=426,000. The structure of this compound was confirmedby mass spectroscopy and by ¹ H NMR spectroscopy.

Part B: Preparation of4-[[2-butylamino-3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]-pyryliumtetrafluoroborate

Butylamine (42 mg, 0.575 mmol) was added to a solution of4-[[3-[[7-diethylamino-2-[1,1-dimethylethyl]benz[b]-4H-pyran-4-ylidene]methyl]-2-methoxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-7-diethylamino-2-[1,1-dimethylethyl]benz[b]pyryliummethosulfate (142 mg, 0.195 mmol, prepared in Part A above) in methylenechloride (10 mL). The resultant solution was stirred at 20° C. for 30minutes, then washed with 10% tetrafluoroboric acid (2 4 mL aliquots),dilute aqueous sodium tetrafluoroborate, and finally dilute sodiumbicarbonate (omission of the sodium bicarbonate wash results inisolation of the dye in a protonated form as indicated by a poorlyresolved NMR spectrum and a bronze cast to the crystals). The organicsolution was then passed through a silica gel pad followed by furtherelution with 10% acetone/methylene chloride (20 mL). The combined purefractions were evaporated to a volume of 7 mL, diluted with MTBE (20mL), stirred at 20° for 30 minutes, and filtered. The filter cake waswashed with MTBE (15 mL) and dried in vacuo to yield the desired dye asa brick-red solid (88.0 mg, 60.6% yield). This dye exhibited aninfra-red absorption at 810 nm in dichloromethane solution, ε=410,000.The structure of this compound was confirmed by mass spectroscopy and by¹ H and ¹³ C NMR spectroscopy, and was found to be identical to materialprepared using a different procedure described in Example 16 above.

Examples 45-51 Preparation of Various Dyes

Example 44, Part B was repeated, except that various amino compoundswere substituted for the butylamine used in Example 44, Part B, thusvarying the nature of the groups R³ and R⁴ present on the 3-substituentof the squarylium ring. The amines used, the groups R³ and R⁴ present inthe resultant dyes, and the wavelength of maximum near infra-redabsorption (λ_(max)) of each dye are shown in Table 1 below. All thedyes were characterized by mass spectroscopy and Table 1 also shows them/e ratio for each dye.

                  TABLE 1                                                         ______________________________________                                        Ex. #                                                                              Amine        R.sup.3 R.sup.4 λ.sub.max                                                                   m/e                                    ______________________________________                                        45   NH.sub.4 OH  H       H       795  621                                    46   CH.sub.3 NH.sub.2                                                                          CH.sub.3                                                                              H       808  635                                    47   n-C.sub.5 H.sub.11 NH.sub.2                                                                n-C.sub.5 H.sub.11                                                                    H       808  691                                    48   (CH.sub.3).sub.2 NH                                                                        CH.sub.3                                                                              CH.sub.3                                                                              827  649                                    49   (C.sub.2 H.sub.5).sub.2 NH                                                                 C.sub.2 H.sub.5                                                                       C.sub.2 H.sub.5                                                                       828  677                                    50   (n-C.sub.4 H.sub.9).sub.2 NH                                                               n-C.sub.4 H.sub.9                                                                     n-C.sub.4 H.sub.9                                                                     828  733                                    51   PhNH.sub.2 (one                                                                            Ph      H       801  696                                         equiv. of                                                                     sodium                                                                        methoxide                                                                     required for                                                                  reaction)                                                                ______________________________________                                    

Example 52 Preparation of4-[[3-[[2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-carboxymethylamino-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumhydroxide inner salt dye

This example illustrates the preparation, by reactions analogous toV→W→X shown in FIG. 5, of the dye of Formula N (FIG. 3) in which R³ is acarboxymethylamino group and R¹ and R⁴ are each a hydrogen atom, thisbeing the dye of Formula I in which Q¹ is a2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene grouping, Q² is a2,6-bis-[1,1-dimethylethyl]thiopyrylium grouping, R³ is a carboxymethylgroup and R¹, R² and R⁴ are each a hydrogen atom. Due to deprotonationof the carboxyl group, this dye exists as an inner salt. The amine usedto form the amine group is glycine.

Part A: Preparation of4-[[3-[[2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-methoxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumtetrafluoroborate

Dimethylsulfate (4.5 mL, 6.0 g, 47.6 mmol) was added to a solution of4-[[3-[[2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-hydroxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumhydroxide inner salt dye (4.50 g, 8.62 mmol, prepared as described inU.S. Pat. No. 4,508,811) in methylene chloride (75 mL). The resultantsolution was stirred at reflux for 6 hours, then allowed to stand for 48hours at 20° C., after which it was examined by thin layerchromatography to ensure complete reaction. (Silica gel plates elutedwith 5% methanol in methylene chloride show the starting dye at R_(f)0.75 (brown fading to green) and the desired product streaking at R_(f)0.1-0.35. A blue impurity at R_(f) 0.9 corresponds to an impurity in thestating material.) Sodium methoxide (7.56 g of a 25% methanolicsolution, 35.0 mmol) was then added dropwise over a period of twominutes and the resulting dark brown solution was left at 20° for 3hours (this treatment with sodium methoxide is intended to destroyresidual dimethyl sulfate, a toxic methylating agent). The reactionmixture was then poured into 60 mL of ice-water containingtetrafluoroboric acid (15 mL of a 48% aqueous solution), and the organiclayer was washed with dilute aqueous sodium tetrafluoroborate, stirredover solid sodium tetrafluoroborate (3.0 g) and silica gel (1.0 g) andthen filtered. The filter cake was washed with methylene chloride (20mL) and the combined filtrates were evaporated to circa 15 mL. Theconcentrated solution was diluted with methyl t-butyl ether (MTBE, 50mL) and stirred at 20° for one hour, during which time a precipitateformed, which was collected by filtration. The product was washed withMTBE (20 mL) and dried in vacuo to provide the methylated dye as itstetrafluoroborate salt (4.69 g, 87.2% yield; HPLC analysis indicated apurity of 99.7% by area at 365 nm). Further dilution of the liquors withMTBE (circa 100 mL) provided an additional crop of 0.232 g (4.3%) of themethylated dye. The dye exhibited an infra-red absorption at 787 nm indichloromethane solution, ε=330,000. The structure of this compound wasconfirmed by mass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Alternatively, the methylated dye may be produced by usingtrimethyloxonium tetrafluoroborate in methylene chloride, thus providingthe desired dye directly as the tetrafluoroborate salt, but theprocedure gives a much less clean reaction.

Part B: Preparation of4-[[3-[[2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-carboxymethylamino-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumhydroxide inner salt dye

Tetrabutylammonium hydroxide (1.5 mL of a 1M methanol solution, 1.50mmol) was added to a suspension of glycine (112 mg, 1.5 mmol) inmethanol (4.0 mL) and the resulting clear solution was charged at 5°-10°C. with4-[[3-[[2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-methoxy-4-oxo-2-cyclobuten-1ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumtetrafluoroborate (624 mg, 0.10 mmol, prepared in Part A above); a browncolor developed. After 35 minutes the reaction mixture was quenched into5% aqueous tetrafluoroboric acid (55 mL). The resulting black gum waswashed with water (40 mL), taken up in methylene chloride (20 mL) andwashed again with water, then evaporated to a red-black solid which waschromatographed on silica gel, eluting with a 15% methanol, 25% acetone,60% dichloromethane mixture, to give 1.0 g of a brick-red partial solid,partial gum. A 300 mg portion of this gum was deprotonated bydissolution in dichloromethane, washing with dilute sodium bicarbonate,evaporation to 2.5 mL, and dilution with MTBE (12 mL). The resultingprecipitate was collected by filtration and washed with MTBE (10 mL),then concentrated under reduced pressure to furnish the desired productas brick-red, fine prisms (91.2 mg, 52.4% yield). Further dilution ofthe mother liquors with MTBE (50 mL) provided a second crop of 53.2 mg(30.6%) of product.

The dye exhibited an infra-red absorption at 828 nm in dichloromethanesolution, ε=285,000. The structure of this compound was confirmed bymass spectroscopy and by ¹ H and ¹³ C NMR spectroscopy.

Example 53 Preparation of4-[[3-[[2,6-bis[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-4-oxo-2-[2-phenyleth-1-ylamino]-2-cyclobuten-1-ylidene]methyl]-2,6-bis-[1,1-dimethylethyl]thiopyryliumtetrafluoroborate

This Example illustrates a reaction similar to that in Example 52, PartB above, but using 2-phenylethylamine to produce a dye having a3-[2-phenylethyl] grouping.

Addition of 2-phenyleth-1-ylamine (from the hydrochloride salt andtriethylamine) to4-[[3-[[2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene]methyl]-2-methoxy-4-oxo-2-cyclobuten-1-ylidene]methyl]-2,6-bis[1,1-dimethylethyl]thiopyryliumtetrafluoroborate using conditions analogous to those of Example 52,Part B above provides the dye N (FIG. 3) in which R³ is a2-phenyleth-1-ylamino group and R¹ and R⁴ are each a hydrogen atom, thisbeing the dye of Formula I in which Q¹ is a2,6-bis-[1,1-dimethylethyl]thio-4H-pyran-4-ylidene grouping, Q² is a2,6-bis[1,1-dimethylethyl]thiopyrylium grouping, R³ is a2-phenyleth-1-yl group and R¹, R² and R⁴ are each a hydrogen atom.

The dye exhibited an infra-red absorption at 816 nm in dichloromethanesolution, ε=276,000. The structure of this compound was confirmed bymass spectroscopy and by ¹ H and ¹³ C spectroscopy.

Example 54 Effect of Deprotonation on Position of Principal Absorptionsof Cationic Amino Dyes

Near infra-red absorption spectra were measured for certain cationicdyes of this invention in a neutral solvent (approximately 3 mL), andthe measurements was repeated for a solution of the dye in the samesolvent with the addition of a strong organic base, DBU (approximately10 mg). The positions of the principal infra-red absorptions areindicated in Table 2 below.

                  TABLE 2                                                         ______________________________________                                        Dye of                                                                        Example                                                                       #         Solvent       λ.sub.max, neutral                                                               λ.sub.max, base                      ______________________________________                                        16        dichloromethane                                                                             797       854                                         17        dichloromethane                                                                             802       866                                         18        dimethyl sulfoxide                                                                          829       897                                         ______________________________________                                    

From the data in Table 2, it will be seen that deprotonation of the dye,presumably from the nitrogen attached to the squarate ring, causes ashift to longer wavelength of the principal infra-red absorption byabout 60 nm.

Example 55 Imaging

This Example illustrates the use of a dye of the present invention in athermal imaging medium and process.

The thermal imaging media used in this Example was a simplified model ofthat described above with reference to FIG. 6. A coating fluid A wasprepared by combining the infra-red dye of Formula IR4 (1.8 mg, preparedin Example 9 above) with acetone (0.73 mL), the leuco dye of Formula LD3above (110 mg) and a polymeric binder (polyurethane Estane 5715,supplied by B. F. Goodrich, 0.73 mL of a 15% solution in acetone).Similarly, a coating fluid B was prepared by combining the infra-red dyeof Formula IR6 above (1.8 mg, prepared in Example 21 above) withdichloromethane (0.18 mL), the leuco dye of Formula LD3 above (103 mg)and Estane 5715 (0.72 mL of the acetone solution). The fluids werecoated onto a 4 mil (101 μm) transparent poly(ethylene terephthalate)base using a #12 coating rod. The films thus formed were laminated at180° F. (88° C.) and 60 psi (0.4 MPa) to additional sheets of 4 mil (101μm) poly(ethylene terephthalate) which had been coated with Joncryl 138(supplied by S.C. Johnson & Son, Inc., Racine, Wis. 53403) to athickness of approximately 2 μm. The resultant imaging media(hereinafter designated Media A and B respectively) exhibited peakabsorptions in the near infra-red at 848 nm, absorbance 0.93 (coating A)and 805 nm, absorbance 1.51 (coating B). Storage of samples of thesestructures at 60° C. for 4 days resulted in losses of only 9.7% and2.4%, respectively, of near infra-red absorptions for Media A and B.

A portion of Medium A which had not been heated was exposed to infra-redradiation from a GaAlAs semiconductor diode laser emitting at 867 nm,which delivered 62 mW to the medium. The laser output was focussed to aspot approximately 33×3 microns in size. The medium was wrapped around adrum whose axis was perpendicular to the incident laser beam. Rotationof the drum about its axis and simultaneous translation of the drum inthe direction of the axis caused the laser spot to write a helicalpattern on the medium. The pitch of the helix was 33 microns, chosen sothat none of the medium was left unexposed between adjacent turns of thehelix. In this arrangement, the exposure received by the medium wasinversely proportional to the speed of rotation of the drum (heremeasured as a linear writing speed at the medium surface). Table 3 belowshows the relationship between writing speed and red optical density(measured using an X-Rite 310 photographic densitometer, supplied byX-Rite, Inc., Grandville, Mich., with the appropriate filter) achieved.The unexposed medium had a red density of 0.07.

Similarly, a portion of Medium B which had not been heated was exposedto infra-red radiation from a GaAlAs semiconductor diode laser emittingat 792 nm, which delivered 151 mW to the medium. Table 3 shows therelationship between writing speed and red optical density achieved. Theunexposed medium had a red density of 0.075.

                  TABLE 3                                                         ______________________________________                                        Writing speed, m/s                                                                           Red optical density                                            ______________________________________                                        Medium A                                                                      0.14           0.48                                                           0.125          0.62                                                           Medium B                                                                      0.43           0.22                                                           0.32           1.54                                                           0.25           2.95                                                           0.18           4.08                                                           ______________________________________                                    

From these results, it will be seen that these thermal imaging mediawere capable of producing images when exposed to near infra-redradiation. Medium B produced images with optical densities as high asthose needed in commercial transparencies.

We claim:
 1. A process for the preparation of a1,3-disubstituted-2-amino or substituted amino squarylium dye of theformula: ##STR19## in which Q¹ and Q² are each a pyrylium, thiopyrylium,selenopyrylium, benzpyrylium, benzthiopyrylium or benzselenopyryliumnucleus, R¹ and R² are each independently a hydrogen atom or an alkylgroup containing no more than about 6 carbon atoms, and R³ and R⁴ areeach independently a hydrogen atom, or an alkyl or acyl group containingnot more than about 6 carbon atoms, or one of R³ and R⁴ is a hydrogenatom and the other is an alkyl sulfonyl group wherein the alkyl groupcontains not more than about 4 carbon atoms, or a toluenesulfonyl group,or R³ and R⁴ together form a hydrocarbon group such that R³ and R⁴together with the intervening nitrogen atom form a nitrogenousheterocyclic ring containing no hetero atoms other than said interveningnitrogen atom,which process reacting the corresponding1,3-disubstituted-2-unsubstituted squarylium dye with an alkylatingagent to produce a corresponding 1,3-disubstituted-2-alkoxy squaryliumcompound, and thereafter reacting the 2-alkoxy compound with ammonia ora primary or secondary amine to produce the 1,3-disubstituted-2-amino orsubstituted amino squarylium dye.
 2. A process according to claim 1wherein the alkylating agent used is a dialkyl sulfate.